The four championship contenders this season can all lay claim to superstars that they originally drafted. Cleveland has LeBron James, Golden State has Steph Curry, Klay Thompson and Draymond Green. San Antonio has Tim Duncan and Tony Parker. And Oklahoma City has Kevin Durant, Russell Westbrook and Serge Ibaka.

At the same time, along the way, all four teams have been involved in trades that allowed them to acquire another star or send one away. On paper, that's how building a contender in the NBA works: it's a straightforward process where you nail your lottery picks, gather enough assets to trade for a star when he is available, hit on a few key free agent signings, and voila, you're contending for a championship.

In reality, though, the process is tricky; it not only requires teams to put themselves in the right position to trade for players or convince them to sign with them, but it also involves luck and a small window to maximize the prime of your key players. Consider the Knicks and Nets, who five years ago this week acquired Carmelo Anthony and Deron Williams respectively. After years of being out of the playoffs, both teams landed the superstar they long coveted, and started their path toward contention. Today, both teams are out of the playoff picture with a murky future. Williams is no longer with the Nets, and Anthony might not be with the Knicks next season.

Those two trades and the team's subsequent process of surrounding their star players with the necessary pieces to contend serve as cautionary tales for teams who are lining up to acquire a star for their own team this summer. Superstar trades and signings themselves fall into their own categories. Here's a look at some of the major acquisitions in the past five years and what we've learned from them.

Category I: Building from scratch

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Feb 2011: Knicks acquire Carmelo Anthony in three-team deal

Feb 2011: Nets acquire Deron Williams from the Jazz

July/ August 2014: Cavaliers sign LeBron James, trade Andrew Wiggins to Timberwolves for Kevin Love

What happened: All of these moves added a superstar to rebuilding programs. The Knicks were 28-26 when Anthony arrived, thanks to Amar'e Stoudemire's MVP performance during the first few months of the season. The Knicks had missed the playoffs for six straight years heading into the 2011-11 season. With Anthony, the team went 14-14, finishing the season at 42-40, and was swept in the first round by the Boston Celtics. In the two subsequent years, the Knicks added Tyson Chandler and J.R. Smith to supplement the Anthony-Stoudemire duo that never quite fit, especially after Stoudemire's play started to decline thanks to age and injuries. The group peaked in 2013, winning 54 games and advancing to the second round of the playoffs.

After acquiring Williams, the Nets finished 24-58, missing the playoffs for the fourth straight season. The following season, the team went 22-44. It wasn't until 2013 that the Nets finally returned to the playoffs in their first season in Brooklyn. After subsequently adding Joe Johnson, Paul Pierce and Kevin Garnett, the team won one playoff series with that core group before being disbanded

Meanwhile, LeBron and Love propelled the Cavs back into the NBA Finals last season, but not before a lot of midseason roster tinkering: the additions of Smith, Iman Shumpert and Timofey Mozgov. Love's fit alongside LeBron and Kyrie Irving has been a constant storyline. The Cavs are once again the best team in the East this season, but they have already fired their coach as the pressure mounts for them to not only return to the Finals, but to figure out a way to stop the Warriors, Spurs, or whoever comes out of the West.

What we learned: All the pieces matter. The Knicks never found the right mix to surround Anthony, and eventually the roster went under a rebuild. Aside from Kristaps Porzingis, there's very little else on the team at the moment suggesting that they have the capability to make a playoff run this season or next. Also, subsequent moves can have a cumulative effect of backfiring on a franchise. The Nets are learning this, having surrendered their next three first round picks in win-now moves. They have been left rebuilding without much in the way of blue chip players on the current roster, and very little they can do to improve aside from overpaying for talent in the open market this summer. A similar situation is unfolding in Cleveland, although at a less alarming rate. With LeBron, the Cavs are still favorites to come out of the East, but the roster tinkering continues. A head coach has been replaced and less than two full seasons into his Cleveland tenure, Love is already at the center of every major trade rumor, which might culminate in him leaving the Cavs this summer if they fall short of winning a title in June.

Category II: Adding a superstar to a strong core group

Dec 2011: Clippers acquire Chris Paul from the Hornets (now Pelicans)

Oct 2012: Rockets acquire James Harden from the Thunder

July 2013: Rockets sign Dwight Howard

What happened: The Clippers had missed the playoffs for five consecutive seasons but had Blake Griffin and DeAndre Jordan on the roster, players who would grow into their prime after the Paul trade. Paul's arrival pushed Los Angeles into the second round in his first season. Since then, the Clippers have won 56, 57 and 56 games, and they're 37-19 this season. With some caveats, they've been a very successful franchise under Paul's guidance. Still, the fact that they've yet to make it out of the second round means that head coach and general manager Doc Rivers might have to blow up the Paul-Griffin-Jordan core this summer

Daryl Morey and the Rockets spent years assembling assets, chasing down free agents at midnight on July 1, and just days before the start of the 2012-13 season, contract negotiations broke down between Harden and the Thunder, allowing the Rockets to swoop in and land the superstar they had coveted. With Harden in the fold, Morey was able to sell Howard on leaving the Lakers to join a contender in Houston. Harden evolved into one of the best individual scorers in the league, and the Rockets made it to the Western Conference Finals last season.     

What we learned: Even when you make the right moves, the window to contend is still short. The Clippers have not been able to navigate around the Warriors-Spurs-Thunder trifecta and are currently positioned to finish fourth in the West, which would set them up for a second round matchup against the Warriors, if they even get there. Beyond the big three, the Clippers have tried and failed again and again to find the necessary supplementary pieces to get over the hump in the West. Meanwhile, Harden and Howard's relationship seems tenuous and the Rockets might not even make the playoffs this season. Howard is expected to opt out of the last year of his deal this summer, and after multiple efforts to trade their starting center at the trade deadline, Morey might move in a different direction to find another star.

Category III: Superstar-impact deals but only in retrospect

June 2011: Spurs trade George Hill for Kawhi Leonard

March 2012: Warriors trade Monta Ellis for Andrew Bogut

July 2013: Warriors trade for Andre Iguodala

What happened: The Spurs were dealing from a position of strength when they acquired first round pick Leonard in exchange for Hill, since they already had Tony Parker at point guard with plenty of years left in his career. Never could they have imagined that Leonard would blossom into a superstar, and win a Finals MVP.

Curry, Thompson and Green should deservedly get the majority of the credit for propeling the Warriors into becoming a historically great team, but the trade for Bogut helped shift the identity of the Warriors and gave them a defensive-minded center to complement their perimeter talent. The acquisition of Iguodala added another dimension to the team, and once again paid off when the Warriors went with a smaller lineup, down 2-1 in the Finals against the Cavaliers. The MVP of last year's Finals? Andre Iguodala, of course.

What we learned: Leonard is by definition a superstar, while Bogut and Iguodala are role players. But in all three deals, the two best teams in the West landed players that became crucial pieces in championship runs. Having superstar talent on your team is key, but nailing these types of trades which transform a franchise and pushes them into championship contention is just as important. This is why conversations about the Warriors signing Kevin Durant this summer (assuming there's mutual interest) are so fascinating. Should the Warriors simply add another star to their core, and sacrifice some of the pieces they've built on their way to possibly back-to-back championships, or do they stick with the roster they have which has been working so well? If the signing does happen, it'll most definitely lead the updated version of this article in five years.

Category IV: The deals you don't make

Dec 2013: Kyle Lowry trade to the Knicks is vetoed, remains a Raptor

July 2014: Warriors discuss Klay Thompson for Kevin Love swap, decide not to make the trade

What happened: Immediately after trading Rudy Gay to Sacramento, Masai Ujiri set upon a full teardown of his roster by negotiating a deal with the Knicks for Lowry in exchange for young assets and future draft picks. The Knicks got cold feet and decided to back away from the deal. How close was this move to happening? Lowry discussed it on J.J. Redick's podcast this week and admitted that he had two duffel bags packed in his Toronto home and was waiting for a confirmation call from his agent to fly to New York. Instead, he stayed, re-signed with the Raptors that offseason, was voted an All-Star starter in back-to-back seasons, and has led Toronto to the number two seed in the East this season

The Thompson for Love swap would have changed the trajectory of not only the Warriors, but the Cavaliers as well. Think about it hard enough, and you wonder who the title contenders would be this season. By not making the deal, the Warriors kept the Curry-Thompson backcourt together, and the rest, well, you're seeing it play out right now.

What we learned: It's true -- sometimes the best deals are the ones you don't make. With the benefit of hindsight, both of these almost-trades fall into that category. It also makes you wonder just how many trades that are seriously discussed but never came to fruition there are, since these are simply two that were more widely reported than the millions of other trade scenarios that are floated around by general managers. There are regrets about making superstar deals, but there is also relief for walking away from them. Like everything about team building, sometimes you just never know until things play out.