Final answer:
Psychodynamic theories share a common emphasis on the unconscious mind and its influence on behavior.
Step-by-step explanation:
The main similarity between all the psychodynamic theories is their emphasis on the unconscious mind. Psychodynamic approaches, such as those developed by Freud and the neo-Freudians, focus on inner processes and the influence of the unconscious on conscious behavior. They believe that buried thoughts, feelings, and repressed memories stored in the unconscious have a significant impact on our personality and behavior.