Back when I worked at Lucent Technologies, a job that I came to hate, I made a rule about Mondays. I was not allowed to miss work on Mondays except for scheduled vacation or for cases of illness. No waking up and deciding I would take a personal day off. No skipping because I was feeling a little out of sorts. I knew that if I ever started avoiding Mondays I'd probably never go to work again and thus become a burden to society.
I don't hate my current job but the Monday rule still applies. It's one of those self discipline things that I do to keep my life running smoothly. I needed it this morning. I didn't sleep at all well last night and would really have liked to just stay home. But being insomniac anyway, I don't consider lack of sleep a legitimate excuse for missing work. So I got up and had some cereal and made some coffee and forced myself out the door.