You Wait Longer Than You Have To
Some things are worth waiting for, but many are not. You should arrive at your appointment on time, and you usually do, but the person who you are to see and gave you the appointment should also see you when he told you.
Medical offices are notorious for making you wait, for what? Was there an emergency or merely overbooking. My limit is one hour. The few times that I went up to the desk and told the clerk/receptionist that I was leaving they were flabbergasted. Of course you shouldn't leave if blood is gushing out of your body but if it's something that can wait just make another appointment and leave. (If you gush blood all over the receptionist she'll get you in very quickly). If everyone who didn't have a true emergency would leave after an hour then the appointment makers would change their schedules/appointments so we would not have to wait - sometimes for hours.