Gestalt psychologists studied how

people see a triangle with missing corners as a complete triangle because of the principle of closure

pairing a neutral stimulus with a stimulus that reflexively produces a response eventually leads to the neutral stimulus producing the response because of the principles of classical conditioning

supporting someone no matter what they do leads to a strong self-concept for the person as a result of unconditional positive regard

dream analysis brings unconscious conflicts to the surface because of psychoanalytic principles