Diffusion of responsibility

Diffusion of responsibility is a social phenomenon which tends to occur in groups of people above a certain critical size when responsibility is not explicitly assigned.

Diffusion of responsibility can manifest itself through the following:
 * in a group of peers who act or, through inaction, allow events to occur which they would never allow if alone (see bystander apathy for an example) or
 * in hierarchical organizations as when, for example, underlings claim that they were following orders and supervisors claim that they were just issuing directives and not doing anything per se.

This mindset can be seen in the phrase "No one raindrop thinks it caused the flood."

For example

 * Kitty Genovese, a New York woman, was stabbed to death near her house. More than 30 of Genovese's neighbors heard her screaming for help, yet no one helped her, each thinking that somebody else definitely would.
 * In a firing squad, one shooter is traditionally given a blank bullet, allowing all members of the firing squad to believe that they only fired a blank.
 * In some electric chairs there may be many switches, one of which is not connected. The executioners may then choose to believe that they were the one who only pulled a non-functional switch.
 * In military terms, it may be easier to deal with the death of an enemy when the soldier receives a direct order to do some action. See below for a discussion on the "I was only following orders" defense during the war-crimes trials of Nazi Germany. The Milgram experiment also demonstrates this principle.

Legal uses
The latter definition was used as a legal defense (unsuccessfully) by many of the Nazis being tried at Nuremberg. It has been used with varying degrees of success in other situations.