Well, humans seem to all have individual motivation systems. Some are motivated by the chance to get rest, others are motivated by getting to be with their friends or eat a food they truly enjoy. By withholding things the human mind craves and then giving it to them when the task is complete, it creates a reward system that usually works as motivation... I actually don't know how this works, because I am extremely unmotivated and can find nothing motivating as well, but I hoped this would be at least a tad... helpful.