Intelligence cannot be present without understanding. No computer has any awareness of what it does.
Quantum mechanics makes absolutely no sense.
As you say, the way string theory requires all these extra dimensions and this comes from certain consistency requirements about how string should behave and so on.
I was indeed very slow as a youngster.
The basic theory in twistor theory is not to add extra dimensions.
People think of these eureka moments and my feeling is that they tend to be little things, a little realisation and then a little realisation built on that.