Rational NBA fans don't think they can physically compete with the game's players. They also realize drawing up plays during timeouts, juggling lineups and taking on every other responsibility a professional head coach has would pretty much be impossible. 

But talk to any knowledgeable fan about the game, and basically all of them think they could do a better job than their favorite team's general manager. They probably aren't right. (But in years past, the most adept basketball aficionados may have had reasonable claims to take over in Toronto, Minnesota, Charlotte, Washington D.C., Brooklyn or Manhattan.)

In reality, the general manager has the most responsibility and the most diversified objectives. They have to master the league's expansive collective bargaining agreement, keep their teams competitive in the short and long term and spend millions of their boss' dollars with confidence and wit. 

Despite the belief of most, building a successful team is actually an extremely difficult task. Here are the NBA's five best general managers working today.

5. Danny Ainge

Boston Celtics general manager Danny Ainge had a rocky start to his tenure in 2003. Under his watch for those first four years, the league's proudest franchise continued to struggle. But the latter half has been a rousing success, and nobody is more deserving of praise for the Celtics' turnaround than Ainge.

He's responsible for one of the most significant trades in NBA history, (true for a multitude of reasons that resonate today, such as it kick-starting the "super team" era, and pushing LeBron James and Chris Bosh to Miami), acquiring Kevin Garnett and Ray Allen to join his then disgruntled All-Star, Paul Pierce.

The biggest reason Ainge was able to make that deal? He's an excellent evaluator of talent. Just look at the 2004 draft as an example. With three first-round picks, Ainge selected Al Jefferson, Delonte West and Tony Allen. A year later he selected Gerald Green, who was included alongside Jefferson in the eventual deal for Garnett. (West was packaged to Seattle for Ray Allen.)

Ainge's strategy all along was to collect assets and then flip them for a superstar. In the summer of 2007, he did it better than anyone.

4. Pat Riley

Part of being a good general manager is being a good salesman, both to prospective players and your fanbase. And nobody is better at this than Pat Riley.

Advanced statistics, savvy trades and top-notch player evaluation/development are all a means to the same end: winning a championship.

Riley might not be the best at any of these things anymore, and his strategy to clear cap space in the "Summer of LeBron" had no independent genius to it. Yet, Riley was the general manager who not only got LeBron James to sign with his team long term, but he also re-signed Dwyane Wade and acquired Chris Bosh.

After that he surrounded those three pieces with vital complements like Mike Miller (who perhaps earned more money than he deserved), Shane Battier and Ray Allen. Fair or not, general managers are graded on their ability to do one thing. And even if his methods aren't as organic or intellectually significant as his peers, nobody is better at winning than Pat Riley.

3. Daryl Morey

Daryl Morey is a mad scientist. He operates in probabilities and analytics more than anything else, and he often treats his players like numerical values instead of human beings. His style is groundbreaking, but it'll also prove to be successful sooner than later.

Morey understands the league's landscape and what it takes to win, so one year ago he tore his franchise down with the hope of either acquiring a superstar in the draft or luring one with the cap space he carefully created.

The result was a roster full of assets other teams might be interested in, and when the opportunity to grab James Harden opened up, he struck.

Now the Rockets still have enough cap space to go after another All-Star caliber player, and they're the youngest team in the league still competing for a playoff spot. Their internal growth combined with whoever is added should make them a title contender within Harden's max contract.

2. R.C. Buford

Nearly all of the bricks used to build San Antonio's basketball empire were laid while R.C. Buford was the team's President or Director of Scouting. While he technically took over as general manager after Tim Duncan, Tony Parker and Manu Ginobili were discovered and drafted, Buford's fingerprints are still all over the franchise's most successful decisions.

His most recent stroke of genius was the decision to flip George Hill (a combo guard/asset he drafted with the 26th overall pick in 2008) to the Indiana Pacers for the 15th pick in the 2011 draft (current starting SF Kawhi Leonard).

Whether or not the move upgraded his team's talent is up for debate, but financially the move gave San Antonio way more flexibility than it would've had if faced with re-signing Hill to a second contract (Hill is currently guaranteed over $40 million in Indiana).

Buford's team is always in contention. Year in and year out. And a big reason why is the culture he's helped create, where stars like Parker and Duncan are willing to take less money to stay. Loyalty is a rare thing in professional sports today, but R.C. Buford has managed to make it his ally.

1. Sam Presti

Some people who aren't so smart will say anyone can do what Sam Presti has done, thanks to Kevin Durant. These people are wrong for a hefty sack of quality reasons, but two stand out above the others: 1) financial constraints, 2) evaluating talent.

Let's talk about the second reason first. Sam Presti did not just draft Durant, sit back and kick his feet up on a coffee table. In 2008 he took Russell Westbrook with the fourth pick (ahead of Kevin Love and Brook Lopez) and Serge Ibaka 24th overall. In 2009 he selected James Harden with the third pick.

These decisions should never be overlooked. For example, the year after LeBron James was drafted, Cleveland selected Luke Jackson with the 10th pick while Al Jefferson, Josh Smith and Jameer Nelson were still on the board. The following year Cleveland did not have a draft pick. It effectively wasted what could've been a special time.

Presti was patient, careful and smart enough to understand the importance of building a team through rookie contacts instead of rushing into Durant's golden years. It was wise team-building, and the results have proven his strategy correct.

Another reason why Presti is the league's best general manager is his ability to navigate through financial constraints. If Presti's bosses held enough financial clout to disregard the luxury tax (like the Los Angeles Lakers or Brooklyn Nets), he'd have no reason to trade Harden, arguably the best shooting guard in basketball.

Instead, he was forced to make a difficult decision, and he did it the best way possible. Now the Thunder are still built to be title contenders through Durant's prime, and as the Heat descend, Presti's positioned his team to rise.