Although it may not have been in that book, I remember him saying somewhere that his goal was to beat his best opponents on their best days. He didn’t want to win: he wanted to play flawlessly, and he always felt he needed the best competition to do that.
Ask yourself: how often do you open yourself to critical scrutiny? How often do you risk embarrassment in trying something new? How often do you seek out the best at what they do, study them, then challenge them? These are all very useful activities.
If you are not seeking out challenges, I think I could say as the converse, you ARE mediocre.
This, in my view, is what Christ meant when he said “I came not to bring peace, but a sword.” Obviously, he did not carry a sword. What he carried was a willingness to challenge smug complacency. And he would not have needed to be the son of God to know that would generate a violent backlash.