If you ask people why they tip, they'll say it's obvious. They tip for good service, of course. It's a reward for a job well done.
But a leading theory on tipping suggests that's not really why we do it.
Studies show that the size of the tip doesn't have much to do with the quality of service. The weather, how sunny it is, what kind of mood people are in, these factors matter just as much as how satisfied the customers are with the service they receive.
Jessica Gibson, a waiter at an Irish pub in Tulsa, Oklahoma, believes that the harder she works, the greater her tips are. Yet she also admits that when she's a customer, she always leaves a 20% tip, even if the service is terrible.
Like most people, Jessica tips pretty much the same amount no matter what. It may vary a little, but it won't not much.
Which raises the question: if we don't tip to get better service, why do we it?
Michael Lynn, a professor at Cornell's School of Hotel Administration and a former waiter at Pizza Hut, says there is another explanation: We tip because we feel guilty about having people wait on us. It's a way of saying: "Here, have on drink on me when you're done working."
This is the social pressure theory of tipping, an idea first put forward by anthropologist George Foster.
This theory explains why we tip some people but not others. We tend to tip in places where we're having a lot more fun than the people who are serving us: bars, restaurants, cruise ships. But we usually don't tip in grocery stores or dentist's offices.
This theory makes sense to Corey Norris, a full-time bellhop who works the graveyard shift at a hotel casino in Reno:
If you are going to ask help for somebody to pull your luggage up to your room at 2, 3, 4 in the morning, are you really not gonna tip the guy? I really do get the feeling that people feel guilty asking for help at such a late hour.
And Corey Norris plays off this guilt. He says if people don't give him a tip, he asks for their claim check tag, the little card the bellhop gives you when you go up to the room and he stays with your luggage.
People usually keep this card in their pocket or their wallet, and Corey says that handing it back to him without any money makes them feel uncomfortable. Most of the time, people end up slipping him a few bucks.
But from the perspective of the person doing the tipping, this can be a really awkward situation. No one likes to feel guilty and it can be hard to know if you've tipped enough or if you've tipped the right people.
Professor Michael Lynn thinks that's the problem:
I think it's quite possible that tipping norms undermine overall satisfaction or happiness. The social pressures people feel to give up money they would rather keep, for them tipping is a net loss. And it's very possible that that net loss exceed the benefits.
Yet if we did away with tipping, restaurants would have to raise prices to pay their staff more. They don't want to do that.
And the servers don't like that idea either. Most of the servers I talked to say they like feeling like they have control over how much money they make. They like working for tips.