The average American man is 5’ 9”. Women are closer to 5’4".

The average 20th-century American president, on the other hand, is 6 foot. Nineteenth-century presidents were still taller, at 5' 10". In fact, in more than half of presidential elections, the taller candidate has gotten more popular votes.

It's no surprise that height is strongly correlated to success in professional sports like basketball, where how high one can reach is an explicit part of winning the game. But it's bothersome to think that we would vote for someone based on a physical attribute that has nothing to do with the job.

Are we heightist?

It sure seems like it. Statistics show that an extra inch of height translates to an average of $1,000 more annual income—the six foot man makes five grand more than his 5' 7" colleague.

On the other hand, it's well-known that Hollywood actors skew short—especially leading males. Robert Downey Jr., America's highest-paid actor at the time of this writing, is below average at 5' 8". Other high earners like Mark Wahlberg, Tom Cruise, and Zac Efron are below average. (One of my personal favorites, Kit Harrington aka Jon Snow, is 5' 8" as well.)

Film producer Brian Hennessey sums up a common explanation:

"The dynamic of 'shorter' actors is mostly a result of practicality. There is more of an abundance of actors and actresses of average height so they are easier to cast. They are also by and large easier to shoot. It is somewhat challenging to frame an actor who is 6 foot 3 inches when the rest of the cast averages 5 foot 9. This is especially true when a male actor is significantly taller than a female actor in a romantic themed story. There is also a number of stars who are uncomfortable working with actors who are significantly taller for fear of appearing too short. They can have a significant influence on the casting choices of a film. Then there is the aspect of taller men by and large choosing to participate sports over performing arts early on in school, thus leaving a smaller pool of skilled taller actors for films."

So, on the silver screen, being tall does not provide an advantage like it does in basketball—primarily because height can be made relative by the camera. And being smaller may make things easier on the cameraman. When you roll in social pressure from established short actors to not appear with tall actors, and the assumption that short people opt for high school drama club instead of volleyball, 6 foot up-and-comers may be at a casting disadvantage.

But all of that appears to be bollocks when you look deeper at the earning statistics. Seven of the top 10 highest paid actors last year are above average, and the majority over 6' 0".

Yikes.

The discussion of heightism and success in America mostly revolves around speculation like Hennessey's. We vote for the tall guy "because height conveys power." The short guy gets the leading role "because he's easier to work with"... except he makes less money and gets worse gigs than the tall guy. What a bunch of discriminating bastards, we are.

Fortunately, that's not true either. A few years ago, three economists, Nicola Persico, Andrew Postlewaite, and Dan Silverman, tackled heightism from a clever statistical angle. Controlling for family background, they looked at workers' heights and earnings—which were correlated as highly as race and gender earning disparities—and then investigated how tall those workers were as teenagers.

That data yielded something remarkable:

"Controlling for teen height essentially eliminates the effect of adult height on wages," they wrote. "The teen height premium is not explained by differences in resources or endowments."

In other words, how tall you are now actually has nothing to do with how much money you will earn; it's how tall you were in high school that matters.

Notably, the economists found that height as a pre-teen or child did not correlate to future success. Only during those crucial, awful, self-conscious pubescent years where we struggle to "find ourselves" does height play a pivotal role in our future earnings.

The crucial difference between more and less successful people, it appears, is not height, but what height bestows at age 15: confidence. And just like getting started in sports early correlates to higher chances of professional success, a confident teenager will do more, get more, and be more confident at age 40 than an anxious one.

This explains the tall presidents: running for president takes shovelfuls of confidence—confidence you likely have had from a young age. Indeed, histories of US presidents—which I documented in Smartcuts re: how success correlates with age and experience—indicate that successful presidents were confident go-getters who had the gall to defy normal paths and procedures.

And the short actors? Success and confidence in Hollywood clearly have snowballing effects on each other; the through-line between the top earning actors, regardless of height, certainly includes confidence. But one overlooked factor in the earnings data is that 8 out of 10 top earners—folks like D'Wayne Johnson and Liam Neeson—are action stars, which movies tend to pay more than other genres. It helps to be big and tough in an action role, but more importantly, top action stars tended to big in high school, too—and not all of them started as actors, but in other careers where confidence was built. Case in point: at 6' 5", The Rock has been enormous from the beginning, and got his start as a professional wrestler out of high school.

The proliferation of confident below-average actors in categories like drama and comedy where short men and women appear to be overrepresented may be explained by adolescent confidence as well. Teen and young adult actors are generally cast as younger than their actual age, and in those roles it pays to be physically smaller. So the small actors get better roles during those crucial confidence-accelerating years, and they go on to successful adult careers with poise. They go on to take more risks and get better gigs.

Once again, success has more to do with our ability to be bold enough to be proactive, to think and act differently, and to step up to the plate than is does with outside attributes.

This is great news. It means we have one less reason to blame success on luck. Because confidence—barring real psychological and medical disorders—is something we can still grow once we're adults.

The bad news is that confidence isn't something we can buy in a store. But what we learn from actors and presidents is that if we want to be more successful, no growth hormone therapy is required. Confidence building—small wins, exercise, anxiety-busting meditation, and/or a good old-fashioned shrink—may once again be the smartest investment we can make in ourselves.

Shane Snow is Chief Creative Officer of Contently. He writes about media and technology for Wired, Fast Company, and more. Subscribe to more stories at http://eepurl.com/yJaEP or follow on Twitter.

If you liked this post, check out the bestselling new book, Smartcuts: How Hackers, Innovators, and Icons Accelerate Success!

"Spellbinding." - Huffington Post

"Worth its weight in 10 airport business books."

-The New York Times

"It's Malcolm Gladwell meets Tim Ferriss."

- Scott Gerber, President of YEC