What have you learned about relationships in your life? (a revived question)

This one was originally asked by the former jelly who went by the name of wundayatta (and several others). Here are his original details from December 9th, 2012:

I’m sure you’ve learned a lot, so let’s narrow it down to the first couple of things that enter your mind. They don’t have to be the best things or most important things. Just any two things you’ve learned over the course of your life.