On the one hand, yes, facing death over and over again, combined with a psychological willingness to accept whatever happens, can probably take a cool headed person and give them nerves of steel. On the other hand, repeated exposure to extreme stress can also destroy a person if they're not inclined to grow stronger from it. I guess my previous point was, I'm not denying that response to stress can be improved, but there's a strong element of talent in being the sort of person willing to strap oneself to a controlled explosive moving at thousands of miles per hour in the first place.
