An excuse seeks to extenuate, sometimes to remove the blame entirely from something which would otherwise be a fault. It can seek to do this in three ways: (a) it can suggest that was is seen as a fault is not really one; (b) it can suggest that, thought there has been a fault, the agent is not really blameworthy because he is not responsible and (c) it can suggest that, though there has been a fault, and though the agent is responsible, he is not really to blame because he has good reasons to do as he did.
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.