If he truly doesn't remember what he was supposed to forget, he doesn't even remember the amnesia suggestion and can take no satisfaction from his success because he is not aware that he has accomplished the posthypnotic suggestion.
"A Practical Guide to Self-Hypnosis"
Melvin Powers
Many subjects feel that they must experience amnesia before they can benefit from hypnotic suggestions.
"A Practical Guide to Self-Hypnosis"
Melvin Powers
Lumping the phenomena of amnesia, somnambulism, hypnotism, anesthesia, obsession and hysteria into the grand group of mental dissociations and disintegrations, he achieved a unification never considered possible before him.
"The Glands Regulating Personality"
Louis Berman, M.D.