This is the same thought I had after reading Justin Kan's post (http://justinkan.com/what-good-is-experience). I was surprised by how much emphasis Justin placed on the importance of experience. I feel one of the best traits of an entrepreneur is the ability to learn quickly and figure things out on the fly.
Having experience doesn't preclude being able to learn quickly and figure things out on the fly. There's a stigma often associated with experienced people that they become slow, complacent, and uncreative. If these traits are seen in more experienced people, I would be willing to bet that it is more of a correlation based on other things that are common in experienced people (having a family, already being wealthy, etc.)
I think it also helps to have (or develop) a high tolerance for ambiguity. You don't really know where you're going, and something may happen tomorrow that upends your business model. You have to be okay with that. I think experience with that process makes it a bit easier to focus on what you can control.
Learn quickly and figure out things on the fly... for ten years. That's experience. :-)
That kind of experience ends up giving you the confidence to attempt hard things that you would never have dreamed you were capable of. But - and this was the point of the OP for me - it always feels like you are faking it and have no idea what you are doing, every single time.
In fact, if it didn't feel that way, then that would probably mean you stopped trying, stopped growing and doing new things and have actually stagnated in a rut.