Diffusion of responsibility
Etymology
From "diffusion" (Latin "diffundere," to pour out) and "responsibility." The concept was developed by social psychologists John Darley and Bibb Latané after the 1964 Kitty Genovese case, in their studies of the "bystander effect."
noun phrase · /dih-FYOO-zhun uv rih-spon-suh-BIL-uh-tee/
The tendency to feel less personal responsibility to act when others are present, assuming someone else will.
What it names
Explains why a crowd can watch an emergency and no one steps in — responsibility spreads thin until no one owns it.
Example
In the group chat of forty people, diffusion of responsibility meant the urgent question sat unanswered for hours.
Related idea
The bystander effect is the observed outcome — people failing to help in groups; diffusion of responsibility is the mechanism inside it, the sense that the duty isn’t specifically yours.