What mistake have you made that you learnt the most from?

Until I learned about active listening, I made the mistake of assuming that hearing was equivalent to listening.
Since I learned to listen attentively, and contextually, I have learned more than I ever dreamed of. There’s a great book that I have used extensively: “People Skills” by Robert Bolton. I recommend that because it’s far more useful than a recent and more popular book “Crucial Conversations”. Much of what is popularly described as Emotional Intelligence can be learned from Bolton’s book.