The phenomenon where people stand witness to a crime or accident but fail to respond because they expect others to respond and do what is necessary. There are numerous instances of the bystander effect every day.
1) The belief and expectation that someone else will take a necessary action and so freeing you from the obligation.
2) A phenomenon where a necessary action is neglected because all those who can take the action expect others to do so.
3) One cause of passivity and inaction.
Example: An individual waits for a scientist to discover a new technology to address CO2 levels in the atmosphere while continuing to live a carbon-intensive lifestyle and continuing to support fossil-fuel dependency. Diffusion of responsibility is one of the contributing factors to passivity in the face of an imminent danger.