Stress
The work itself is a one out of ten. The stress of paying your bills on your miserable salary will keep you up nights, but that's really just a by-product of the job.
The most stressful aspect of the gig is that you'll be on your feet all day, occasionally dealing with rude, mean, and unreasonable customers. Get Dr. Scholl's for your tootsies and practice your phony smile. Beep.