Idea problem?

I hate it when this happens. But sometimes when I get in the middle of a project idea. I have another Idea of an application that is 10X exciting than the one I am doing. then I am compelled to do the second idea and leave the first one.

And later I realize than they are equally interesting and quit second idea and go back to first one but now I am so out of the zone with first idea that I just go back to doing second idea and wait for another idea to pop up

This really has me having alot of incomplete projects. How do you focus on one project at a time