And because you told me about it before I found out about it, there was no punishment. That was our deal!

This is a good rule.

I feel that we as humans know we should learn from other's mistakes, but our ego gets in the way to ensure most of us don't. We think we know best or better, and often especially of the ones closest to us. "How can you be an expert in A, when I know you suck at B?"

My wife does the same with me. She won't take advice on something others pay me for, because she knows I leave my dirty clothes on the bathroom floor sometimes.