Which of the following is a common defense mechanism?

Repression is considered a common defense mechanism in psychoanalytic theory, primarily developed by Sigmund Freud. It involves unconsciously blocking out painful or uncomfortable thoughts, memories, or feelings from awareness. This psychological process serves as a protective function, helping individuals manage anxiety or distress by keeping these intolerable emotions submerged in the unconscious mind. As a result, while the individual may not consciously recall or acknowledge these repressed feelings, they can still manifest in various ways, such as through dreams or psychological symptoms.

The other options, while related to coping and emotional management, do not fit within the classical definition of defense mechanisms. Negotiation typically refers to discussions aimed at reaching an agreement, while coping pertains to the strategies individuals employ to handle stress or difficult situations. Reflection involves thinking deeply about one's experiences or feelings and does not inherently serve the same protective function that repression does. Therefore, repression stands out as the most representative of a defense mechanism in the context of the theory of personality.