We learn while we teach.

Where this comes from

Seneca wrote this to Lucilius nearly 2,000 years ago. He told him to spend time with people who make him better and with people he can make better, because it works both ways: we learn while we teach.

How you could say it to a five-year-old

“Teach me the game you made up. I bet you’ll think of a new rule.”

Seneca, Letters 7.8. We put these lines into plain English ourselves, staying close to the original and to public-domain translations.