Nor do I. I think it's a combination of things, habits formed from playing games late as a kid is one, but I think that wanting to solve a problem enough to stay up late for it is another. As is a natural procrastinating spirit that many developers have. I get my best work done between 12pm-2am because I finally STOP INTERRUPTING MYSELF. When it's just me finishing that user story that's standing between myself and sleep, I tend to stop going on reddit.