When it comes to sports, no player is ever perfect. No matter how good an athlete you are, there are balls you can't reach, attackers you can't catch, shots you can't reach, etc. It's physics, it's reality, and much as we wish it wouldn't, it sometimes intrudes on our little world. However, these are physical mistakes. Everybody is going to make physical mistakes, and these are easily forgiven.
Mental mistakes on the other hand, are an entirely different animal. Most mental mistakes are avoidable, and usually pretty easily so. Flying into a challenge with both feet off the ground 80 yards from goal in the first ten minutes of a Champions League match is certainly avoidable. Doing so twice, in the first leg of the biggest match in your club's history, is downright stupid. As Peter Crouch trudged off the pitch today, the fans at the Bernabeu Stadium chanted, "Tonto, Tonto!" This means, "Stupid, stupid!" I see no reason to argue with them.