This x100000. This is fundamentally it; just like how we love to talk about 10,000 hours and targeted practice, so too can we extend this concept to startups. You just have to throw (and attempt) a bunch of ideas at the wall until one of them sticks, and learn along the way.
I used to get so bent out of shape that my side project wasn't a massive success or that I'm not a young prototypical YC founder straight out of college on the fast track to entrepreneurship. When I took a step back, realized that most founders (even outside of the tech bubble) are older than 35, and have tried (and failed) at a lot of different startups...you then embrace that it's just all about executing and learning from as many projects as possible. It takes out a lot of the stress and anxiety about succeeding, and instead using your side projects as practice to get you to that great idea in your future.