Stress
You really have to hustle, and that can wear you out. You also have to deal constantly with a collection of the most conceited, ignorant, superficial individuals you'll ever have the displeasure to meet, and that can wear thin. You have to please your client, you have to please producers, you have to please the bagel delivery boy. You laugh, but within a week, that bagel delivery boy could be somebody important, and he could have your butt.