This, and also a good organization system (this is very subjective... What works for me probably wouldn't work for 99% of people) to make it easy to come back to a project when you eventually feel like working on it again.

Edit: honestly disposable income is a huge part of this. I finally have money to buy things purely for organization, I have extra space where I live, and I don't feel guilty about the money I spend on new hobbies.