I had not thought of it in quite those terms. It also explains something for me. When I created my character Robert, I gave him all the powers he could want - in other words, if he imagines he can do it, then he can. I wondered at my doing something so stupid, for how can he remain interesting if he is so powerful (he even enters a black hole wearing instruments, so as to help the scientists...and comes out again).

I had not realised two aspects of his gift which would limit him. With time and experiences, he would find it much more difficult to imagine himself having whatever power he needs (and becomes ever more reluctant to acquire more powers, for he fears he could become a tyrant or else, mankind might give up and die out because they cannot fight him - so he teaches others how to fight him) and...this is where your comment comes in, he is 100% vulnerable to those he loves.

In a sense it is paradox; the stronger we are, the more we need to have (good) weaknesses so as to remain human.