Being friends with someone is totally different from creating something together. Even as business partners, conflict will inevitably happen when two people work together. The majority of them are minor, but eventually you'll settle on something you're quite convinced of and won't alter your mind about, such as the direction the company is taking, its compensation, how much money is being allocated, etc. As the stakes rise in importance, the emotions rise as well. Money has an impact on people's lives. They grow defensive, resentful, and maybe vindictive emotions. It is not recommended to mix business with friendship because doing so would probably end the friendship.