Quoting Arsene Wenger

"The common denominator of successful teams is that the players are intelligent. That does not always mean educated. They can analyse a problem and find a solution. The common denominator of a top-level person is that they can objectively assess their performance. You speak to a player after the game and ask him to rate his performance and if he analyses well, you know he is the sort who will drive home thinking, "I did this wrong, I did that wrong". His assessment will be correct and, next time, he will rectify it. That player has a chance. The one who has a crap game and says he was fantastic, you worry for him. This is also true in life beyond football."