Excuses take many subtle and devious forms. They are often chronic evasions of responsibility borne of irrational fear. One of the human animal's main and most dangerous tendencies is said to be that of trading survival for peace of mind. Excuses are one of these methods. Excuses prevent insights into personal problems and thus bar healthy change in personality. They are generally used to hide human fragility. Many lies invoke self-defence (the avoidance of harm to oneself) in the form of excuses.