The most important thing for sustaining a long term programming side project is to work on regularly, ideally every day even if it is just for 10 minutes. This

The most important thing for sustaining a long term programming side project is to work on regularly, ideally every day even if it is just for 10 minutes. This keeps the current state and the next step of your project fresh in your mind which makes it much easier to pick up each day. You avoid that "now where was I exactly?" hump. It also means that you're making constant progress, even if that progress is slow. And it also mitigates any enthusiasm sapping guilt you may develop because you've started that project but have ignored it for too long.