What's something you would say to someone who didn't believe in your entrepreneurial vision?

Well its depends on his mind if he don't want to listen you as per your expectations then no one on earth make him believe.

I would ask them to take a deep breath. Let go of all their assumptions and beliefs. Listen to the idea like a child and tell me how they feel. People are the most honest when they are children that believe in the power of hope and dreams.