What does it take to succeed? This question has fueled a long-running debate. Some have argued that humans are fundamentally competitive, and that pursuing self-interest is the best way to get ahead. Others claim that humans are born to cooperate and that we are most successful when we collaborate with others. But what if, rather than being hardwired to compete or cooperate, we had actually evolved to do both? And how can we unpack the psychology of when and how to interact with people as our friends and our foes, and use this knowledge to get the best outcomes in life?