Human error
Human error is an action that has been done but that was "not intended by the actor; not desired by a set of rules or an external observer; or that led the task or system outside its acceptable limits". Human error has been cited as a primary cause and contributing factor in disasters and accidents in industries as diverse as nuclear power (e.g., the Three Mile Island accident), aviation (e.g., United Airlines Flight 173), space exploration (e.g., the Space Shuttle Challenger disaster and Space Shuttle Columbia disaster), and medicine.