Well, not so much "mental toughness". But alot of his problems are deffinatly mental. Compare him to a guy like Greg Maddux, who does not have near the "stuff" of Carlos. Maddux is a very smart pitcher. I have to assume Zambrano is not. Maddux is very calm and follows his game plan. Zambrano when something, even a minor setback, before the game gets out of hand. He looses it mentally. Not so much "looses it", but he does not do the right things and let's his emmotions ruin his game. He needs to take a step back, slow his game down. Take a few breaths, and concentrate only on the next pitch. This is one of his big downfalls. And it can certainly be considered something like "mental instability" on the mound. losing it mentally = not mentally tough prior is more mentally tough than zambrano has ever been. when the pressure was on, prior dominated down the stretch in '03 and was great in the playoffs. zambrano was atrocious that postseason. but b/c prior is quiet and now injured, he's the guy who is a basketcase. go figure.