The Ultimatum Game, in which test subjects respond to take-it-or-leave-it offers, has allowed psychologists to explore how humans handle issues like fairness and punishment

But a new study shows some people attempt to punish even when the rules of the game are stacked in a way that makes it impossible

Game theory has provided researchers in a variety of fields, from psychology to economics, an opportunity to test human behaviors under controlled conditions. It allows big questions—are humans rational actors when money's on the line

humans aren't purely rational when it comes to monetary decisions, as they appear willing to make financial sacrifices in order to punish others in the name of fairness

A paper that will appear at PNAS this week takes things a step further and shows that people will still reject unfair monetary offers, even when the only one they punish is themselves