Final answer:
Denial is a defense mechanism that involves not believing that a problem exists. It is a way to protect oneself from anxiety or distress.
Step-by-step explanation:
The defense mechanism that involves not believing that a problem exists is denial. Denial is a defense mechanism in which an individual refuses to acknowledge the existence of a problem or the reality of a situation. It is a way to protect oneself from the anxiety or distress that would arise from facing the problem.
For example, if someone is confronted with evidence of their spouse's infidelity but refuses to accept it and insists that everything is fine in their relationship, they are using denial as a defense mechanism.
Other defense mechanisms include repression, rationalization, and projection. These mechanisms serve to protect the individual's ego from threatening or uncomfortable thoughts, feelings, or impulses.