the people always put greater value on whichever reward they started out with

Half chose the mug,and half chose the chocolate.That is, they seemed to value the two rewards similarly.Other students were given a mug first and then a surprise chance to swap it for a chocolate bar,but only 11% wanted to.Yet another group
started out with chocolate,and most preferred to keep it rather than swap.In other words, the students nearly always put greater value on whichever reward they started out with.Part of this has to do with how quickly we form connections between our sense of self and the things we consider ours.That can even be seen at the neural level.