I cannot overstate the importance of diversity in startup teams. Having a diverse team is crucial for long-term success.
Too frequently, I see people who are too similar trying to start companies together. Maybe they were college roommates, close friends, or even family members. They have very similar backgrounds and experiences. This leads to serious blind spots and challenges down the road, some of which are fatal.
Unfortunately, investors propagate this bias. Some investors have an image of the perfect founding team as two technical people who are best friends, college roommates, and have known each other for years. Despite a few notable successes, these types of companies are statistically less likely to succeed. (I encourage both VCs and aspiring founders to read “The Founder's Dilemmas” by Noam Wasserman, which covers this topic in depth.)
I view startup teams as the foundational DNA of a company. Founders should be deliberate in selecting the DNA they want in their company's "gene pool." Just like in biology, a gene pool that is a monoculture accentuates all traits (positive AND negative) leading to blind spots (pathogens) that can kill your company. Friends often share the same networks, biases, and blind spots, resulting in a tendency to hire similar people. Over time, even if they stumble across someone with complementary skills, the organization will reject them. (e.g. “Why should we hire her? She can’t even code!”)
This is why at Inception, we place a strong emphasis on collaborating with individuals who differ from you. You want to work with people who bring diverse skill sets, experiences, and backgrounds, yet share common values, ambition, and vision for the future.
Moreover, founding a company with someone you've recently met isn't as unusual as it might seem. One crucial element of a cofounder relationship is the "spark" of working together, which can occur just as easily with a new acquaintance as with a long-time friend.
Consider the analogy of marriage, which is not too different from being a cofounder. (In fact, you will probably spend more time with your cofounder than your actual spouse!) Most people don’t end up marrying their lifelong childhood friend or (gulp!) relative. More often, people marry someone they've known for a (relatively) short period because they were able to form an immediate strong connection. The same principle applies to choosing co-founders.