He experienced repression of those painful memories, making himself forget what had happened.

repression 由前缀 re-（表示"再次"或"向后"）和词根 press（按压）组成，加上名词后缀 -ion。字面意思是"反复按压"，引申为"压抑、压制"的心理防御机制，指无意识地抑制痛苦记忆或冲动的过程。