I think it's important to be honest with oneself about the motivations for starting a business with somebody else. From what I see, some entrepreneurs don't want to go it alone because they believe there's safety in numbers. If you're leaving a good job, have a family to take care of, etc., it can be easier to convince yourself that you're doing the right thing if someone else is taking the plunge with you.

This is a really bad excuse for bringing on a co-founder. In my opinion, it's a primary reason you often see bloated founding teams comprised of individuals who have similar skills, not complementary skills.