It was who he was. He wanted to kill everyone because he had so much resentment and anger. For others it was a sport, for him it was his way of expressing his inner demons. So that stayed with him a long time. I think what might have broken him is his kid dying on that treadmill.His animalistic mindset is what made him such an intimidating opponent. The other fighters already lost the fight in their mind before the first punch was thrown. You can't just turn that switch off when now you have a sexy little lady in front of you if you are Mike Tyson in his prime.