In the context of group processes, social facilitation refers to the tendency for the presence of others to improve a person's performance on simple or well-learned tasks. Conversely, social inhibition (or social impairment) describes the tendency for the presence of others to worsen performance on complex or new tasks.

The underlying psychological mechanism, largely explained by Robert Zajonc's arousal theory, is that the mere presence of others creates physiological arousal. This arousal enhances an individual's dominant response—the response that is most likely to occur in a given situation.

For social facilitation, if the task is simple, familiar, or well-practiced (e.g., a seasoned musician playing a simple piece), the correct response is dominant, and arousal improves performance. For example, athletes often perform better in front of a cheering crowd.

For social inhibition, if the task is complex, novel, or difficult (e.g., a novice public speaker or learning a new skill), the incorrect response is more dominant, and arousal makes errors more likely. A student might fumble a complex calculation when being observed.

Both phenomena highlight how the social environment significantly impacts individual behavior and performance within group settings, not just through direct interaction but even through mere co-presence. Understanding this helps in designing optimal learning and work environments.