There was a poster in the the hallway of my middle school that said 'Shoot for the Moon: Even if you miss, you'll land among the stars.'
I always hated that poster.
My cynical eighth grade self, thought "It should read: 'Shoot for the Moon: If you miss, you'll slowly suffocate to death in the cold loneliness of space.' " Cynicism aside, it seemed patently false. Success wasn't about shooting for the moon, but doing your homework, studying for tests and not being a dick to your friends.
As I've gotten older, I think I understand the idea behind the poster a lot better. Those without high ambitions fail to achieve high results. However, I think that my adolescent objections still stand. While it's all very well and good to 'aim high,' it still matters quite a bit exactly what you are aiming at. For example, if you start a company, it may fail, but you will still have learned valuable skills and have new connections and street-cred. However, if you drop out of school to try and become, say, a pro baseball player, your chances of success are far lower and you are left with far fewer options if you do not succeed with your primary goal.
To put it in tersms of start-ups, it's hard to see which companies are going to be wildly successful, but, generally, it's much easier to see which are definitely not going to be. Over confidence, poor thinking of the market, over-reliance on magical 'technical' solutions, over-reliance on name-dropping connections are all bad signs. What is amazing is that if you hang around Silicon Valley or any other large tech community long enough, you start to see the exact same mistake being made over and over again.
This leads me to believe that most companies and people fail to succeed because they continue to make the simple fundamental mistakes. I think this is why we see people that 'create their own luck.' Once you've mastered the art of not screwing up, success is simply a matter of searching through that remaining 20% to see what sticks.