Answer:
Psychoanalytic theory.
Explanation:
The psychoanalytic theory can be considered the most valid because it has as main objective to explain the human mind through the full comprehension of the subconscious, and can even find an explanation for the existence of several mental problems, through factors that the patients did not have knowledge of, or they didn't remember that they were in their minds.
This theory is based on the understanding that a person's psychic processes are often unconscious and difficult to be visualized only through the dialogue between therapist and patient.