If I worried about "likelihood of not finishing a project" before I started a project, I would never start. First step is to start, if you get there then you can worry about finished or unfinished - either way you will likely have learned something or created something which is more than the worried non-starter can say.
Agreed. Starting projects which you won't finish just consumes resources and therefore prevents other projects from getting finished. I have been very aware about this. Being highly selective on projects which you even start is simply being smart.