It kinda depends on the project. With things that take a lot of time and personal development, v think learning a language, it is more of a start and stop cyclical thing. I get inspired to study Russian and boom, it's day and night for a few weeks all my free time goes to that. Then it dies off and I move on to something else.
For things that do not allow for that kind of flexibility, I have to talk myself into starting and I then know that I have a day or a few to knock it out hardcore like. Generally a few days of concerned effort is enough to tackle must projects. If not, there is a non-zero chance it will get dropped when I get bored.