"Mistakes teach you more than success" was something I heard and put almost no stock in for quite some time, but I really do believe it's true. When something fails you can observe the results or catch the problem in real time and determine what's gone wrong and make adjustments; when something succeeds without failures or breakdowns it's difficult to know if it's what you did that caused success, or if it was other factors outside of your control or measures. It can take a while to learn how to be open and accepting of those opportunities.

The only failure is the failure to learn the lesson

There was a teacher who said "it's only a failure if you haven't learned from it" and I might not have taken it to heart if she hadn't also told me "it's better to be a smartass than a dumbass". These days I'm very glad to have figured out how to handle what I haven't figured out yet.