It has taken me years to grasp this. Even though I know it to be true. I’m always stunned.

“Wow, that guy is short.”

“That girl is way shorter than I expected.”

This applies to actors (the former couple of Edward Norton and Salma Hayek come to mind), and to athletes who aren’t pro basketball players — the only people in the world uniformly even taller than you thought.

Hockey players are far shorter than you think, and ballplayers aren’t far behind.

The shorter-than-you-think thing applies in particular to world-class gymnasts.

Sunday night, I watched some of the U.S. Olympic Trials for the women’s team … which wasn’t quite an accurate title for the thing, given that only two women actually were assured spots on the team.

But it reminds me, having interviewed gymnasts in the mixed zone of several Olympics … that they are just remarkably tiny. The men, yes, but the women … just itty-bitty.

Shawn Johnson, reigning world champion, is 4-foot-9. Which puts her at the bottom of the team roster, but not by a whole lot. Samantha Peszek is hardly any bigger.

Chellsie Memmel is 5-foot-2.

And Nastia Luikin, the “tall, willowy” one?

Also 5-foot-2.

Anyway, no matter how short you might think Olympics gymnasts might be … they’re even shorter.

What does this mean? Nothing? Well, other than there must be a competitive advantage, in gymnastics, for women around 5-foot-nothing, and men about 5-6.

(Funny thing? The U.S. Olympic Committee website doesn’t list heights or weights for its male or female gymnasts. Matter of fact, I’ve just spent several fruitless minutes trying to find out the heights of the other U.S. elite gymnasts. Shawn Johnson’s height comes up only because she stands out as short among short people, and reporters mention it. Liukin’s height was mentioned on imdb.com — because she has done some Hollywood work. Memmel’s height came up on an obscure site.)

Mostly, we get back to the general expectation most of us regular folks have that anyone “famous” or “athletic” is somehow bigger than we think. It’s us expanding them … or diminishing ourselves.

The truth is, they almost always are smaller. And gymnasts are at the far end of this “truth.”