Enthusiasm is an engine, it drives you forward, gives you get-up-and-go – but an engine doesn’t work so well when your wheels are pointing four different ways.
If you don’t make conscious choice about what you’re going to pursue, (and, more importantly, what you’re NOT going to pursue), the lack of constraints will cause your projects to atomize. Spread too thin, your enthusiasm will explode into everything and nothing at once, exhausting you and accomplishing nothing. Your wheels will be pointing four, seven, two hundred different directions. Smell that burning rubber?
If you’re a natural enthusiast, you job is to be content with less excitement (because projects in process are always less exciting than projects in abstract), less huge swings and agonizing crashes, less chaos. Systematically reduce the amount of projects you’re doing, reduce the amount of projects that you say “yes” to, and ship every project, even if it’s boring and you hate it and you can’t stand to work on it one more second and the new shiny project is just so appealing.
If you do, you’ll have time to think, time to learn, time to polish and improve. You’ll make better stuff, and you’ll actually finish things.