For starters, the very job title describes how tough a waiter's job is. Someone who 'waits on people'. It can be tiring and annoying and frustrating and, for the peanuts that they get paid, they show a great deal of patience while putting up with all the shit customers give them.
Waiters manage many tables at once. From taking orders to delivering them to keeping tab while keeping an eye out for every customer's need, they're experts in multitasking!
Putting up with a customer's every demand and accommodating every kind of person that shows up is a challenge in itself. But waiters do it every single day!