We all know we get cranky when we haven't had anything to eat, so what I found most fascinating about the paper was the idea that our willpower is a limited resource. It takes brain resources to maintain self control, and each act diminishes our mental reserves. This phenomenon is known as "ego depletion", and was pioneered by psychologist Roy Baumeister, based on an experiment he conducted in 1998. He and his team found that subjects who resisted temptations also reduced their ability to persist in completing a subsequent task. He surmised that, like a muscle, our self-control and willpower can be strengthened or weakened depending on our physical condition. It can also be influenced by social factors, such as personal motivations or the ever-important perceived need to fit in with a group. You've seen ego depletion in action anytime you've slowly worn somebody down to go to a concert with you or drive the getaway car in your latest heist.