When you blast right threw opponents, that gave Ali helll and then Ali just toys with you and takes your power, that you just destroyed the same fighters in their prime that gave Ali tremendous legacy fights and this Man is talking trash and laughing at your punching power and then knocks you out, this would destroy anyone, being a professional and one of the most feared Boxers ever and this isn't like Tyson vs Douglas, it's not even close, this was the biggest upset in boxing history at the time and both had no distractions, both were 100%, unless Ali was starting to get sick, then it's even a more incredible achievement from Ali, but that's another story.
It's just the way it was supposed to happen, Gorge gets humbled and embarrassed and comes back older and wiser and shocks the world, wins the Heavyweights title and becomes even more beloved and sells the hell out of those grills, that they paid him a billion to advertise.
Gorge Foreman story, going from unstoppable, to being humbled, to winning the title, breaking a record and ruling the world in entertainment and being beloved, is a movie and life story, only made up in books.