Stress
You don’t make a career out of losing races. If you don’t perform well and win a certain number of times, you’ll lose your sponsorship (your ride). No car, no competition. It’s common for a driver to change sponsors and cars from year to year depending on how well he performs, how much money he can convince the sponsors to part with but the bottom line is that he has to win.
It’s impossible to look at this job as anything but super high stress. Air traffic controllers probably have less stress than NASCAR racing drivers. Not only do you have to worry about winning and keeping your job, you need to worry even more about surviving the race.
If you can’t stand the heat, get outta the cockpit.