Ask HN: How do you get past the intellectual curiosity phase?

Usually when I am initially starting out a hobby project (an app or a tool) there is a great enthusiasm initially to learn something, but once I “figure out” the core of the problem (mental dialogue “so this piece fits here to do this, and if I extend this with some more polish it will work this way”) and can extend the idea mentally to completion, interest immediately drops leading to an unfinished project. How does one force\motivate themselves to implement the small things to finish projects?