If you would be a good reader, read.

Where this comes from

Epictetus taught that we become what we do again and again. If you want to be a good reader, read, he said, and if you want to stop getting angry, stop feeding the anger. His student wrote it down about 1,900 years ago.

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

“Want to swing all by yourself? Every swing teaches your legs.”

Epictetus, Discourses 2.18. We put these lines into plain English ourselves, staying close to the original and to public-domain translations.