I love and believe in what I am working on, I usually can’t wait to get out of bed and start programming, and that’s exactly why I force myself to stop after a reasonable number of hours. Because I know 80 hours a week (or 40 hours a week) of programming would not be sustainable for me. That much work would simply destroy my life outside of work and harm my productivity at work. Short-term gain, possibly, long-term loss, inevitably.