Beating yourself into the ground is not a form of exercise. If you’re trying to build muscle and/or burn fat, hitting the gym day in and day out eventually catches up with you. And both beginners and advanced guys can fall into this trap. The beginner isn’t content with progress, so the more-is-better philosophy kicks in. While the advanced athlete might know the value of a good night of sleep and days off, sometimes the drive to keep pushing takes over. Either way, overtraining leads to injury and incredibly horrible irritability. Listen to the body, take days off, and get more sleep.