50% of it is having a better app. If you believe in your idea, invest your time to make the best app you possibly can.

50% of it is having better marketing. Just because there is an app with a head start doesn't mean you can't start marketing in your social networks (both real and virtual) and online (not necessarily paid for either)

Quality, will often win out, if you have the better app.

If.

Corollary - it's all about the execution, not the idea.