A research study concluded that servers in restaurants increased their tips by providing a token gift: a fancy piece of chocolate delivered with the check.
That's right, a simple, small and unexpected act of generosity made customers happy. In addition, the size of the generosity has an effect on happiness, as an offer of two pieces of candy increased tips more than an offer of one piece of candy.

Not only that, the study also showed that offering one piece of candy, and then offering another piece, led to greater tips than just offering two pieces in the first place.