Knowledge is a funny thing. Once you get it, as long as you keep using it, and remember it - it's yours. It's the direct opposite of a material good. If I buy a really nice bottle of wine, or a cool t-shirt with a shark on it, eventually the wine's gone, the t-shirt faded from wear and use.
But when you learn something, the more you use it, and share it, the more completely it becomes yours.
On Friday, my co-worker C. and I were reviewing some code together, when I saw something he'd put in a controller. "Oh," I said, "that's really business logic, and should be in a service, I think."
I only really learned the distinction myself a few jobs ago. But it's stuck with me. I feel really, really good about it.