I must admit it's one of my bad habits.
I'll be working on a song and typically have an idea that i record in a new song or write down and then never finish.
Even worse are those brilliant intros or verses that you create and then can't do anything else with.
I read a songwriting tip that said the way to break it is to stick with the song until you finish it. Don't worry where it takes you because regardless of how it ends up sounding you may find new styles, sounds or techniques you wouldn't have otherwise used.
That sounds like good advice to me!