The bystander effect explains why people are less likely to help when others are present. When more people are around, responsibility gets spread out, and each individual feels less personal obligation to act because they assume someone else will intervene. The situation also tends to feel less urgent in the moment, since people look to others to judge what’s happening (pluralistic ignorance), which can further dampen the impulse to help. The combination of diffusion of responsibility and reduced perceived urgency makes helping less likely as the group size grows. Other theories describe different motives for helping but don’t capture this specific dynamic. Social Exchange Theory focuses on weighing costs and benefits of helping, which can explain why someone might help or not in particular contexts but not the general drop in helping when bystanders are present. The Reciprocity Norm is the expectation that helping others will be rewarded by future help, and Equity deals with fairness in outcomes; both address willingness to help in a broad sense but not the reduced likelihood that occurs simply because more people are around.