Reading and experience train your model of the world. And even if you
forget the experience or what you read, its effect on your model of the
world persists. Your mind is like a compiled program you've lost the
source of. It works, but you don't know why.
[R]eading and experience are usually "compiled" at the time they happen,
using the state of your brain at that time. The same book would get
compiled differently at different points in your life. Which means it is
very much worth reading important books multiple times.
-- Paul Graham. "How You Know" (December 2014)
http://www.paulgraham.com/know.html