You can go many years without doing certain things, and then when you do them again you haven't forgotten anything and it's as if you've been doing them all along. It's proverbially like riding a bicycle; it just so happens that literally riding a bicycle is like that too.

Certain other things you tend to forget after 15 or 20 years. For instance, you may forget that you can scrape up your elbow and knee pretty badly when you fall off your bicycle. You can also forget how a big ol' scab is kinda gross but also kind of a weird little badge of honor, proof that you are a physically active person. Most of all, you can totally forget just how unnervingly compelling it is to pick at your scabs after 5 or 6 days when they start healing, and also that you really shouldn't do that because it makes you heal really strangely and unevenly.