Its stamina.
No there isn't some higher level of understanding or deep perception. Every one of the all time great programmers had 1 exact thing in common with no exceptions. Stamina. You will not find a single outlier.
They did their craft every day, for many hours, year after year.
So sure, any of us could have taken the individual small steps. But when you look at a whole body of work, you'll see they're cranking through these "small steps" like the Juggernaut running through walls for decades