You may not want to hear it, but your critics are often the ones telling you they still love you and care about you, and want to make you better.
Another way to be prepared is to think negatively. Yes, I'm a great optimist. but, when trying to make a decision, I often think of the worst case scenario. I call it 'the eaten by wolves factor.' If I do something, what's the most terrible thing that could happen? Would I be eaten by wolves? One thing that makes it possible to be an optimist, is if you have a contingency plan for when all hell breaks loose. There are a lot of things I don't worry about, because I have a plan in place if they do.
I was hugely impressed... was the ultimate example of a man who knew what he didn't know, was perfectly willing to admit it, and didn't want to leave until he understood. That's heroic to me. I wish every grad student had that attitude.