I have a bad habit of staying up late at night to work on personal projects. It's the only time I feel that I have to myself. My work demands so much of my day. My commute/exercise routine (yes I bike to work) demands even more time. My wife demands hours more; Time that I am happy to give, yet time nonetheless.
This subsequently means that I have little time for myself and my personal projects. Which means my deep desire to work on something for myself has to take time out of something else. That something else is my sleep.