This is completely alien to me. I've had various personal projects over time. They are always managed in terms of goals and available resources and never deadlines. Deadlines can happen, but in general they are a terrible way to manage nearly any development. Better to consider goals and resources and work from there. My results have been pretty good and often open up new potential direction for continuation projects afterward.

There is a saying that works of art are never done, people just eventually quit working on them. Even that seems somewhat apart from "... finishing a personal project you’re doing just for yourself is impossible" which seems overly broad and very dark.