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When you have a finished working game, you are half-way done. And 90% of the work takes 10% of the time. If you want a good game, you have to polish and polish and polish and never stop polishing. I think this is what I read about Jetpack Joyride (a game I love more than Temple Run). I just don't have whatever it takes to stick with it and polish my games like I should.
And yes, I've heard that you have to have something like 10 games before you will start to earn much money. I'm not sure if that is because it pays to have a lot of titles or because after 10 games you finally know what you are doing.