I do about 30 chin-ups at the gym several times a week. I don’t like doing chin-ups, and I couldn’t do them for many years. I’d try and try and couldn’t quite get myself up over the bar.

Then, a crazy thing happened one day: I did one. After doing one, I found that doing a second one was easier. In the space of a few weeks, I jumped from none to more than a dozen. I didn’t develop some supernatural strength or find a new training program.

What changed was that I figured out that I could do chin-ups. Before I did my first one, I never believed I would ever get to the first one. O...