Social facilitation and social loafing are two contrasting effects that the presence of others has on individual performance, and the key difference lies in whether people are performing individually (with others watching or working alongside them) versus contributing to a shared group effort.
Social facilitation refers to the tendency for people to perform better on simple, well-learned, or dominant tasks when others are present—either as an audience or as co-actors doing the same task—compared to when they are alone. The presence of others increases physiological arousal, which enhances the likelihood of the dominant (most practiced) response. This helps on easy or familiar tasks (like running a familiar route or doing simple arithmetic) but can actually hurt performance on complex, unfamiliar, or difficult tasks, because the dominant response in those cases is more likely to be an error—a pattern sometimes called social inhibition or impairment.
Social loafing, by contrast, is the tendency for individuals to exert less effort when working collectively in a group toward a common goal than when working alone, especially when individual contributions cannot be identified or evaluated separately. This happens because responsibility is diffused across the group, and people may feel their personal input matters less or won't be noticed, reducing motivation. Classic examples include reduced effort in tug-of-war or group brainstorming tasks when individual output is pooled rather than measured separately.
In short, social facilitation involves individual performance being observed or paralleled by others (arousal typically boosts effort on easy tasks), while social loafing involves individual effort being pooled into a group product (reduced identifiability typically lowers effort on tasks requiring collective contribution). Factors like task difficulty, accountability, group cohesion, and whether performance is evaluated individually or collectively help explain when each effect is more likely to occur.