Imagine that you're working late at night on a project due in the morning. Your body is tired and your mind is numb, but this project must get done, so you push on. You continue to work, despite the distinct feeling that the project would be much easier if you went to bed and approached it again in the morning. You feel obligated to do it now, so you stay up until the wee hours of the morning, producing less than desirable work in much more time than it would have taken with a rested mind. This was likely not the wisest move, since not only productivity was lost, but quality as well.