I have heard him say, in a documentary, exactly what @RareDenver wrote above: that if he had not had to cope with such extreme physical limitations, he would not have been forced to think about things in the way that he has done. The sheer lack of access to certain tools drove him to a more visual approach that led to new discoveries and conclusions.
But the capacity was always in him or he couldn’t have accomplished what he has.
He might at any time have decided that it was all too much for him, but he persisted. That’s the lesson I hope we can learn. Most of us are capable of much more than we do.