… for a reward than children who thought about sad things or rewards during the test.

Children with cheerful thoughts were able to think about: “You can also think about singing songs, or playing with toys, or anything that is fun to think of. ”

Children in the sad group thought: “You can also think of falling down and getting a bloody knee which hurts a lot, or you can think of crying with no one to help. You can think of anything that makes you unhappy.”

Mischel W, Ebbesen EB, Zeiss AR.; “Cognitive and attentional mechanisms in delay of gratification.”; J Pers Soc Psychol. 1972 Feb;21(2):204-18.