On May 9th of this year, The Boston Celtics defeated the Philadelphia 76ers in game five of the conference semifinals, ending the Sixers’ season. It was a tough loss and a tough series, but the Sixers have plenty of reasons for optimism: it was their first playoff appearance since 2011, their two best players are in their second and first (healthy) seasons, respectively. Joel Embiid and Ben Simmons already look like the real deal. They also have clear avenues to get better: Markelle Fultz missed almost the entire season with a mysterious shoulder ailment, young players like Dario Saric and Robert Covington figure to improve along with the superstars, and they have the #10 pick in the 2018 draft. The Sixers, everyone is sure, will be back.

Two weeks later, the Celtics lost a heartbreaking game 7 to the Cleveland Cavaliers, coming the closest of any Eastern conference team to knocking off LeBron James in the last five years. The Celtics too have every reason to think they’ll return- two of their three best players in the Sierra were rookie Jayson Tatum and second year player Jaylen Brown. They have two in their prime stars, Kyrie Irving and Gordon Hayward, who missed the series with injuries but figure to be back next season. They have another all-star in Al Horford. Those five guys might combine to be the best starting unit outside of the Warriors next year- and behind them, they have even more talented youngsters like Marcus Smart and Terry Rozier, and they still have a treasure chest of future draft picks to round out the roster. The Celtics, everyone is certain, will be back.

Flashback six years though, to the 2012 NBA finals, and you’ll see something that gives you pause. You’ll see Russell Westbrook, Kevin Durant, Serge Ibaka, and James Harden- all 25 or younger — dejected after their loss to the Miami Heat. While the loss stung, most observers agreed the Thunder were, if anything, ahead of schedule in reaching the finals with such a young core. And while LeBron James won this round, he and Durant were sure to do battle for years to come. The Thunder, everyone was sure, would be back.

They never did make it back. Injuries, misguided trades and bad signings, and inexplicable performances at the most important moments led to OKC never winning the championship — or even getting back to the finals — that once seemed assured. Six years removed from what was supposed to be the first of many finals appearances of a dynasty, Russell Westbrook is now the only player player still left on the team from those halcyon days. The Thunder may well end Westbrook’s career without ever reaching the promised land of an NBA championship.

The Sixers and the Celtics both hope for a plethora of future titles, but they’ll need to avoid the pitfalls that tripped up Oklahoma City. Here are the lessons they can take from the Thunder’s failure as the pursue their own dynasties:

1. You aren’t going to get as many shots as you think

It’s really, really, really hard to make the NBA finals, much less win one. Today, with the open road rising up to meet them, the future looks like sunshine and rainbows for the Celtics and Sixers, just as it did for the Thunder six years ago. Things always happen that you don’t expect. Here’s what happened to the Thunder in the years following their lone finals appearance.

2012-13: #1 Seed in the West. Better, more mature, more balanced, even after the departure of James Harden in the offseason. Russell Westbrook is injured in the opening series against the Rockets; the Thunder fall to Memphis in the second round.

2013-14: 2 seed in the West. Serge Ibaka is injured in the conference semis. The Thunder reach the conference finals and go down 2-0 to the Spurs. Ibaka returns and the Thunder knot the series before losing in six games, falling in OT at home in the decisive game.

2014-15: Westbrook and Durant both miss significant time due to injury, with Durant missing nearly the entire season. The Thunder finish 45-37 and miss the playoffs by one game.

2015-16: Fully healthy for the first time since their finals run, the Thunder finish third in the West under new leadership in Billy Donovan. They reach the conference finals and storm out to a 3-1 lead against the 73 win Golden State Warriors, only to squander fourth quarter leads in game 6 and 7. Durant departs for Golden State in the offseason and Ibaka is traded, ending the era.

The Durant-era Thunder effectively had a 5 year title window. They ended it with one finals loss, two conference finals losses, a conference semifinals loss, and one season where they missed the playoffs entirely. Twice, their season was derailed due to injuries to their stars (thrice if you count Ibaka’s injury in 2014). Twice they lost to the team that won the finals that year (The Heat in 2012, the Spurs in 2014). For all 5 of those seasons, they were one of the 3 or 4 best teams in the league. And they wound up with one finals appearance and zero trophies to show for it.

Winning is hard.

For all the potential the Celtics and Sixers show, they too could end up with just one real shot at the crown. They’ll have to contend with each other for one thing, and at some point another contender that no one sees coming will emerge. At the beginning of OKC’s title window, if you remember, the Golden State Warriors were an afterthought at best and a joke at worst. They won 23 games in that strike-shortened season, Steph Curry missed most of the year with injuries, Klay Thompson averaged 12 points a game, and Draymond Green was a Michigan State undersized swingman with little apparent NBA upside. Six years later, Golden State, not Oklahoma City, is the dynastic franchise. There’s no way to prepare for such a team arising, but both these franchises have to be aware that there will be legitimate obstacles in their path to the finals besides each other.

All this is to say that whenever either team makes the finals, they need to be ready to win that year. OKC was not ready when they reached the Finals in 2012 — their stars were too young, and their veterans were role players at best. The Celtics are ready already, with Danny Ainge very close to achieving his goal of a team that can contend for a decade. Their current big three- Irving, Hayward and Horford- could be the nucleus of a title team, albeit one that has yet to actually see all three dress in the postseason. Conservatively, they would be underdogs against Golden State and Houston.

However, once those three begin to age out, Jayson Tatum & Jaylen Brown will be ready for their star moment. And if the torch passing happens sooner than anticipated, if Tatum is clearly the best player on the team in 2 seasons, then Gordon Hayward is your 4th or 5th option, and if Gordon Hayward is your 4th or 5th option, you’re a championship-level team. Tatum, Brown and Horford were a win away from the finals without Kyrie and Hayward. Adding them back means the Celtics are ready to win a championship even if Tatum isn’t ready to be the best player on a championship team yet. Until he is ready, he and Brown fulfill dual roles: the future of the team and important role players. The Celtics are ready now, and they’ll be ready in 5 years too.

Bill Streicher-USA TODAY Sports

The Sixers, borne of a different team building process (sorry) don’t have the mix of stars in their prime and future superstar youngsters. Instead, their two best players right now, Simmons and Embiid, figure to also be the best players on the team in 2023. In that respect, they are like the Thunder.

If the Sixers ran back a similar roster next year and advanced to the finals (perhaps LeBron moves west and the Celtics are injury stricken again, or perhaps Embiid and Simmons are good enough to beat Cleveland and Boston either way), would they beat Golden State? Probably not. But what if they were to add Paul George? Or Kawhi Leonard? Or LeBron himself? The Sixers in theory can add a max player this summer, either by trade or signing them as free agents. Adding a top five player like LeBron or Leonard would make them true contenders next season, and George would get them close. Without them, the Sixers remain a good playoff team, but not true contenders until Simmons or Embiid takes another leap (or a guy like Fultz becomes a star in his own right). How long does that take? Maybe just one season, but maybe two, or even three. Missing three years of contention would leaves the Sixers with a very short title window. That makes this offseason perhaps the most important one in determining the next five years for the Sixers.

2. You can’t have too many superstars

OKC’s ownership will never admit it, but it always comes back to the James Harden trade.

Whatever the causes that we know or don’t know, OKC traded away Sixth Man of the Year Harden to the Rockets, forever changing the trajectory of both franchises. OKC already had 3 guys who projected to be stars — Westbrook Durant and Ibaka — on max deals. Some people maintain that keeping Harden wouldn’t have changed OKC’s fate- Westbrook, Harden and Durant all need the ball a lot. Harden, the thinking goes, wouldn’t have become the player he has if he’d stayed, or if he had, he, Westbrook and Durant wouldn’t have been able to figure out how to play together.

Bologna. Sure, it can be hard to figure out how to win with 3 superstars who have stylistic overlap. Know what’s way, way harder? Winning with only two superstars. Even if Harden became only 75% of what he is now in OKC, you would much rather have him spotting up in the corner on Russ/Durant picks and rolls than Dion “I’m open” Waiters. Having a third star ballhandler would have allowed for even more staggering of OKC’s stars. Harden could have moved into the starting lineup but subbed earlier than Durant and Russ and continued his old duty running the the second unit. Three superstars is always better than two.

I say three is better than two, not four is better than three, because by the end of his OKC tenure, Ibaka wasn’t the star people projected him to be. He was still a big part of their identity, a good shooter on offense, a top notch rim protector on defense, a mean rebounder who helped Steven Adams dominate on the glass, and one more long switchable body on a team full of them. But he wasn’t a star, and he felt just a bit overstretched in the role of third best player on a championship team. Where he would have been perfect was the 4th best player on a championship team, which is what he would have been, had OKC held on to Harden.

Boston and Philadelphia should both be wary of one of their young studs having an Ibaka like career trajectory- peaking around age 23-24 instead of the expected 27-28. In Ibaka’s 4th year he led the NBA in blocks, posted a career high in points and rebounds, and had a true shooting percentage above 60%. After that, he never got much better. He didn’t really get notably worse either; he simply stagnated. If Jaylen Brown and Ben Simmons have similar career paths, they won’t be bad players- but they won’t be capable of being the second star on a championship team.

There’s no way to predict an enticing young guy who suddenly plateaus. The only way to prepare is to take as many cracks at getting a superstar as possible, so if one guy falls off, you aren’t left hanging. In this light, last year’s trade between Boston and Philadelphia looks like a momentous one for both franchises. Boston agreed to trade the #1 pick in the 2017 draft for the #3 pick in the same draft and a future first round pick, which is going to end up being the 2019 Sacramento kings pick- a pick that could be very, very good (If it goes #1 overall it will revert to Philly). Boston turned 1 crack at finding a supertsar into 2, all while getting the player they wanted anyways — Tatum. Getting the Kings pick also gave Boston the confidence to trade another future draft pick, the 2018 Nets pick, for Kyrie Irving once he became available. Philly, meanwhile, gave up one future shot at a superstar to move up and take Markelle Fultz, who missed almost his entire rookie season with a mysterious ailment that his camp and the team gave conflicting reports about.

Fultz might still end up becoming the superstar Philly thought they were getting. If he never reaches that level though, Philadelphia will need to pursue other avenues for finding one. There’s free agency this year, as discussed, and there’s the results of this year’s draft- Zhaire Smith and the Miami Heat’s 2021 first round pick. This trade is exactly the kind of move a team aiming to get superstar talent makes- Smith has a higher upside (but also a lower floor and longer development curve) than the player Philly traded for him, Mikal Bridges. And that 2021 Heat pick might well be a lottery pick. One bite at the apple gets turned into two- a very Sam Hinkie style move from Philly, and a reason aside from burner accounts to be glad that Bryan Colangelo is gone.

If Philly finds a third star through free agency, the roster will start to get expensive. Boston already is about to run into this problem. Kyrie, Hayward and Horford all make max money. Marcus smart is about to enter restricted free agency this summer, and Terry Rozier will do the same next summer. Boston will need to pay to keep both of those guys, and they’re not even the superstars. Kyrie will be ready for a new contract next summer, and the team will be looking to lock up an extension for Brown then as well.

Paying the luxury tax once is one thing, and that’s what makes OKC’s failure to just extend Harden so boneheaded- they would have only paid the tax for one season before the cap spike (which, to be fair, few saw coming). However, paying the tax for years on end is a different matter, and at some point Boston will have to make a choice. Tatum and Brown will both be max contract guys. Unless Horford takes a discount, Boston faces the prospect of paying 5 guys max deals by 2021. Hayward’s contract expires at the end of 2021, the same time Tatum will go from a cheap rookie deal to handsome max.

If Tatum and Brown develop as Boston hope, it could be tempting to let Hayward go, or trade him before then-particularly if that Kings pick next year turns into another promising young stud. When exactly Boston transfers from it’s current big 3 to its future stars depends on how the older players age and the younger player develops, but Boston will have to be careful how they time it. Jettison Hayward or Kyrie early, and you might lose a season if Tatum or Brown aren’t quite ready. But if you extend those guys and they begin to level off with age, you’ll be stuck paying those guys a ton of money that could go to filling out a winning roster around Brown and Tatum. Which brings us to the final lesson to be learned from OKC.

3. Your supporting cast still matters

Superstars are the most important ingredient in winning a championship, but elite role players are important too. J.R. Smith, walking meme though he may be, nailed a couple of huge 3’s for the Cavaliers in game 7 of the 2016 finals. Andre Iguodala won the finals MVP in 2015 for his work defending LeBron and nailing the shots he was given (yes, he probably shouldn’t have won MVP. He was still important enough that Golden State wouldn’t have won without him). Ray Allen- not LeBron or Dwyane Wade- hit a clutch 3 that saved the heat in game 6 of the 2013 finals, even though he was no longer a superstar. Without him, the Heatles era might have ended with only one championship. The list goes on and on.

OKC never found the right cast to put them over the top or, even charitably, the right mix of the players they did have. But specifically, the Thunder have, for whatever reason, have never been good at finding good shooters. The 2015-16 team had exactly two above average 3 point shooters who saw consistent minutes in the regular season: Kevin Durant and Anthony Morrow, the latter of whose lack of ability do do pretty much anything besides 3’s left him mostly unplayable in the playoffs that year.

By the time of the playoffs, OKC was down to 4 players getting any significant minutes besides the core trio of Westbrook, Durant, Ibaka:

• Steven Adams, young, clean-shaven, but already a force on the glass and a monstrous screener
• Andre Roberson, an elite wing defender with a very limited offensive game
• Dion Waiters, the man who never met a shot he didn’t like
• Enes Kanter- a low post star offensively who’s defensive struggles limited him to 10 minutes a night

In those four guys, you see the failure of OKC’s team building around its star trio. Adams and Roberson were acquired as a result of the Harden trade; both were and are good players, but obviously neither had the impact that Harden might have. Waiters and Roberson were the only wings OKC felt comfortable playing outside of Durant, highlighting Presti’s inability to ever find a good shooting guard following the trade of Harden. That severely limited OKC’s lineup flexibility, curtailed their ability to play Durant at the 4, and meant OKC played the entire series against Golden State with a cramped floor.

Kanter, meanwhile, was supposed to be the final piece of the championship when he was acquired. OKC had a fairly valuable asset- Reggie Jackson, who was an intriguing point guard prospect at that time- who they wanted to get off before his first contract as he and Russ weren’t a good long-term fit (Presti was 100% right about that). The trade that sent him out netted the Thunder Enes Kanter- a young, offensively gifted big man who would take some of the scoring load off Russ and Durant. The thunder threw a big contract extension at him in the summer of 2015 following the trade, only for Steven Adams to start ahead of him for the entire regular season. A guy getting paid $16.4 million a year should be getting more than 10 minutes a game in the most crucial series of the season, but Kanter’s lack of defense made that impossible.

OKC wrung all it could out of those guys. Roberson, a career 25% 3 point shooter, hit 8 of 18 attempts and scored off some great backdoor cuts when the defense ignored him completely. Adams stepped up big on the glass and famously withstood swinging limbs from Draymond Green. But Waiters justified the coaching staff’s lack of trust in him by shooting 35% from the field for the series, and Kanter was mostly ineffective. OKC could and should have still won the series- they were up 3-1, and had a chance to win both game 6 and 7 had either of Durant and Westbrook been able to make a shot down the stretch. But having one more guy they could’ve relied on might’ve been enough to push them over the top. One more good shooter on the floor could have opened up a little extra room for Westbrook and Durant on drives. One more competent ballhandler could’ve given the offense a little extra verve. One more guy who wasn’t Dion Waiters could have made the difference. Superstars matter most, but your supporting cast does still matter.

Boston and Philadelphia have done a great job finding those kind of role players who can actually contribute in the biggest moments. Boston has Marcus Smart and Terry Rozier, two young guards who don’t project to reach superstar levels but can be important players on championship rosters. “Scary” Terry ran the offense effectively in the absence of Irving (and Smart) in the postseason, and is also a good enough off-ball player to get minutes alongside Irving, particularly in Brad Stevens’ egalitarian offense that thrives on multiple ball handlers. Smart is the ultimate glue guy, an elite defender who makes all sorts of winning plays- drawing charges, saving loose balls, clutch steals- at the biggest moments of games. He will probably never become even a good shooter, but it doesn’t matter. His skill set is more varied than Andre Roberson’s, and Brad Stevens has found much more creative ways to involve role players than Scott Brooks or Billy Donovan ever did (coaching, by the way, is another edge Boston and Philly both have over OKC).

At some point, Boston will have to jettison either Rozier or Smart as everyone starts to get paid, and replace those guys with cheaper options. Boston’s track record is encouraging in that regard- players like Evan Turner, Jae Crowder and Shane Larkin have all been rescued from the scrap heap by Danny Ainge and turned into real NBA players. And other homegrown guys, like rookies Daniel Theis and Semi Ojeleye were already able to contribute their rookie seasons as bench guys. We haven’t even mentioned Robert Williams, Boston’s pick in this year’s draft at #27, who already projects to be more talented than that draft spot. And they’ll have a chance to add another blue chip prospect next year.

Philadelphia has two young guys — Robert Covington and Dario Saric — who could be important role guys on a championship caliber team. Of course, if they are the price Philly pays to get Kawhi Leonard, Philly will pay it in a heartbeat. Then they’ll be challenged to fill out the roster with guys good enough to win a championship with without the aid of high draft picks or much cap space. Philly too has an encouraging history- Covington and TJ McConnell were both undrafted guys who were real contributors on a 50 win team last season. Right now, Philly has 2 superstars and a supporting cast that feels about good enough. If they can acquire their third star by internal development (Fultz, Smith) or outright signing them (PG, LeBron) they’ll be in great shape, maybe needing one more top level rotation player to complete the team. If they need to resort to a trade to find that third star (Kawhi, CJ McCollum) they’ll be challenged to rebuild the rotation- but that’s a price well worth paying for an extra star.

The biggest challenge of team building — acquiring young superstar talent — has already been accomplished by both Boston and Philadelphia. But the Thunder will eternally stand as a reminder that nothing is guaranteed in this league. To succeed where OKC came up short, these teams will need to nail the rest of their roster building decisions moving forward. The clock is already ticking, and time could run out sooner than we all think.