OpinKerfiBjarni
OpinKerfiBjarni on Hacker News
I'm failing to come up with a link at the moment, but I remember a widely circulated bit of folklore about how an unnamed engineer within Google set up a cronjob that anonymously e-mailed the entire team a single number every day. After a while people figured out that the number was the byte count of the front page, the implication was that it was a metric that needed to be watched carefully.
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.