Coke Machine vs. Slot Machine

So today at school, my teacher thought it would be fun to enlighten our class on something I thought was pretty interesting. Greeeaaattt. Anyways, he explained to us that when coke machines take people's money, they tend to try the machine one or two more times before giving up. He proposed that the idea of a coke machine is expected to give you the drink of your choice every time you slip your money in. When it fails, people lose hope. Person wants something out of the drink machine, puts money in, person expects to get a coke and doesn't, and person doesn't want to try again for fear of losing money. He compared this scenario with a slot machine.  Person wants something out of the slot machine, person inserts money, person is almost guaranteed not to get anything back, and person continues to keep trying and keeps losing money. Isn't that funny to think about?! hmm... one of things the world may never know...