This sentence means that feelings are fragile and can't stand injuries. There is no pain that goes deep into the bone marrow. No one's heart
From "Zhang Chunhua-Three Kingdoms Kill", it means that people love someone because they can't let go of pain. You hurt, and you betrayed you inadvertently, or hurt you for a long time, or you gave up everything as you grew older, and forgetting things is not resentment.