Social facilitation
The mere presence of others sharpens easy tasks and wrecks hard ones.
What it means
The tendency for the presence of other people — as an audience or as co-actors — to enhance performance on simple or well-learned tasks while impairing it on complex or novel ones. Zajonc's resolution of early contradictory findings was that the presence of others raises physiological arousal, which strengthens the dominant response; for easy tasks the dominant response is usually correct, but for hard tasks it is usually wrong. Later accounts add evaluation apprehension (fear of being judged) and attentional conflict as contributors beyond mere presence. It matters because it shows that something as minimal as being watched systematically reshapes effort and accuracy.
Examples
An expert pianist plays a familiar piece better before an audience but fumbles a piece they are still learning.
One of the first psychology experiments found children wound a fishing reel faster when another child was reeling alongside them than when they worked alone — a simple, well-practised task.
An experienced cashier scans quicker as the queue builds, while the trainee at the next till, still hunting for produce codes, fumbles more the longer the line watches.
First described in Triplett (1898); Robert Zajonc's drive theory (1965).