There's fundamental physiological difference. It's not clear there is. Consider this part of the article: Yet Honnold ended up scared, really scared, on Corr

There's fundamental physiological difference. It's not clear there is. Consider this part of the article: Yet Honnold ended up scared, really scared, on Corrugation Corner. He clung to the big, friendly holds. “I overgripped the shit out of it,” he says. Obviously, though, he didn’t give up after that first experience. Instead, Honnold donned what he called “mental armor” and crossed the threshold of fear again and again. “For every hard pitch I’ve soloed I’ve probably soloed a hundred easy pitches,” he says. One by one, acts that had seemed outrageous to him began to seem not so crazy: soloing moves in which he hangs only by his fingers, for example, with his feet swinging in the open air, or, as he did in June on a notorious route called The Complete Scream, climbing ropeless up a pitch that he had never ascended before. In 12 years of free solos, Honnold has broken holds, had his feet slip, gotten off-route into unknown terrain, been surprised by animals like birds and ants, or just suffered “that fraying at the edges, you know, where you’ve just been up in the void too long.” But because he managed to deal with these problems, he gradually dampened his anxieties about them. So was he born this way, or through repeated exposure did he train himself to be this way? Or, more likely, is it a bit of both? The article certainly seems to suggest that we can all improve on our ability to manage fear... perhaps not to the degree Alex has, but enough so to allow us to tackle challenges that might otherwise seem insurmountable.