The business side of this is cold and harsh, as it always is.

But as far as keeping a friend? He's a teacher, right? Why don't you sell him on the idea about learning how other startups succeed? I'll never forget reading "A Good Hard Kick in the Ass" several years ago. It completely changed the way I understood how startups work. Perhaps you could sell him on the idea that you're feeling a little frustrated, and perhaps other teams out there have learned something that might be useful to you guys.

I also liked "Founders at Work" which I read a while ago. I wouldn't bury the guy in material -- after all, if you give him too much he'll just blow it off. But I'd find some text that made the case and _was presented by another person who is an authority_. That way, it's not a you vs. him deal, it's just a couple of friends discovering how things work.

Good luck. If he's smart and your friend I'm sure he'll see the value of a structured approach to creativity. The trick is to be non-confrontational. Let the ideas battle it out, and not the people.