If someone utters "people never change" ?
People change all the time. But somehow they stay the same.
My impression is (1) the underlying nature of the person remains the same in the long term (2) the masquerade adopted remains the same in the medium term. So in all practical purposes in interpersonal relations the other person does not change. A change to the act is possible by means of affection, intimidation and other emotional effects. Trauma blasts away the mask.
(2) Millon (Freudian)
After trauma, people often feel they are a different person. The event(s) has stripped away their dignity (more likely their survival mask) and revealed their true selves. Unfortunately, he is a stranger. More importantly, the mask was adopted by the pressures of the world is (dys-) functional in the real existence to obtain income.