Final answer:
Rationalization is the defense mechanism used when a patient offers excuses to justify behavior, protecting self-esteem and managing anxiety.
Step-by-step explanation:
When a patient has several excuses or reasons for his behavior, the defense mechanism he is using is likely rationalization. This involves creating plausible but untrue reasons to justify one's behavior, to avoid facing the true, often uncomfortable motivations or feelings behind them. Rationalization helps protect an individual's self-esteem and is one of many unconscious defense mechanisms that can operate when a person is confronted with anxiety. Other defense mechanisms include denial, projection, displacement, and reaction formation.