Stress
Well, you can imagine. Lots. Tonnes (metric), even. Things can go very right, or they can go very wrong, and often there is little you can do about it either way. You're a projectile in this gig in many ways of elements you can not control. While you're waiting to find out which way the pendulum is going to swing, it can be pretty nerve-wracking. After all, this is your reputation on the line.