The Köhler Effect
Groups usually dampen individual effort. Under one specific condition they raise it, and the person who gains the most is the one least able on the task.
In 1926 Otto Köhler had members of a Berlin rowing club hold up a weight until their arms gave out, first alone and then in pairs. The weaker man in each pair lasted longer than he had on his own.
A meta-analysis of 26 studies covering more than 2,100 people put the effect at g = 0.72, a large one, and pinned down the condition that produces it.
The condition is task structure. When the group's result is capped by its slowest contributor, that person's effort becomes the entire outcome and everyone can see it, themselves included. Under that structure the least capable member on a task works measurably harder than they do alone. Pool the contributions instead, so any individual shortfall disappears into an average, and effort drops. That version has a name too: social loafing.
The same person, in other words, loafs or lifts depending on how the work was assembled.
The nudge: Take a project where someone has quietly gone flat. Check whether their piece is visible and whether the result genuinely waits on it. When the answer is no, you are looking at a structure, not a person.
Source: Weber & Hertel, Motivation gains of inferior group members: A meta-analytical review, Journal of Personality and Social Psychology (2007)
