Huh? What kind of friend tosses you aside because you decide to start a company? That makes absolutely no sense. I'm trying to imagine this conversation:

You: I'm starting my own company!

Friend: I think that's a crazy idea. You'll probably fail.

You: I'm confident I can do it.

Friend: I disagree, and we're not friends any more.

If anything, friends usually way underestimate the difficulty of running a business and just throw platitudes at you like, "Do it! Follow your dreams! With passion you can't fail!"