Side projects die because your initial enthusiasm wears off and you start to realize that you are midway through a project that you initiated for your own self

Side projects die because your initial enthusiasm wears off and you start to realize that you are midway through a project that you initiated for your own self amusement and it's no longer making you happy. Don't beat yourself up about walking away. It doesn't mean that you are a quitter and you'll never accomplish anything. It means that you need to find something more important to do. Important tasks are self-justifying; you don't have to talk yourself into working on them. When you find yourself on something important, your motivation will come. You will see it all the way through. In the case of Facebook, I think it must have felt important, because it saw instant success around campus. Once you see that something is generating success, even on a relatively small scale, that starts to validate its importance and you can rationally consider increasing your commitment.