In my long study of happiness, good habits, and human nature, one thing I’ve concluded is that we’re more similar to other people, and also more different from other people, than we imagine.

We often under-estimate how common a behavior, belief, practice, or preference is—and we also over-estimate how common behavior, belief, practice, or belief is.

Here’s an example of how it’s easy to under-estimate how widespread an assumption or behavior is.

I remember talking to someone about habits related to using public restrooms. (I’m very interested in people’s habits, but why we happened to be exploring that particular angle, I have no idea!)

She told me, with modest pride in her ingenuity, “I always want to use the least-used stall in a public restroom, so I never choose the first stall. I pick one in the middle.”

I had to break the news to her. “Actually, research shows that it’s the stalls in the center get the most use!”

She thought she was making a choice to outwit everyone else, and everyone else was doing exactly the same thing.

We’re more alike, and more different, than we think.