> It sounds like a contradiction that someone could learn something new by answering a question. Isn’t that just spitting out something they already know?

A while back I started participating actively on Reddit's r/explainlikeimfive, and this has been my experience — explaining things I (think I) understand in ways that are accessible to laypeople really forces me to confront the sloppier parts of my understanding. If you're a technical person, it's also a great exercise in communication with non-technical people.