I'm guessing: There will always be people who think they know why your idea won't work. It's in the nature of the game (http://www.paulgraham.com/swan.html http

I'm guessing: There will always be people who think they know why your idea won't work. It's in the nature of the game (http://www.paulgraham.com/swan.html http://www.paulgraham.com/swan.html etc). Founders who take these people's opinions seriously are more likely to give up.