Manny was an energy fighter that overwhelms opponents with physical fury,non stop action and a super high work rate. Those type of fighters burn brightly and look invincible but when the energy levels drop they become human and vulnerable. The give away that his time at the may come to an end was when politics as a career was getting into his mind. Energy fighters like Tyson have to train like demons to stay on top when they let things slip they slip.
With Roy his problems all arose when he dropped down weight from going up to heavyweight. The big weight change and coming down in weight changed him and had a big physical effect on his punch resistance.reactions and how his body behaved. It was the big up and down in weight he went through that messed him up. That was the big unforeseen price he had to pay for gaining the heavyweight championship.