Ingroup favoritism towards people in our own group over those in other groups can happen due to a visual bias called outgroup homogeneity. This bias makes it harder for us to tell apart strangers from different groups. A study suggests that when people play games like the prisoner's dilemma, where they decide whether to cooperate or not, they tend to favor their own group because of this bias. However, increasing the benefits of working together, having more diverse groups, or making the social rules stricter can help lessen this favoritism between arbitrary groups.