Yeah - my experience is that most startups (including my own) really do fail because of the founder's stupidity, but it's very hard to avoid that stupidity even if you know this. There're so many balls you have to keep in the air as a founder, you're bound to drop some of them. It's only after you've practiced through a few failures and can instinctively avoid some of the more obvious failure modes that you start having a reasonable chance of success.