Several researchers determined that the opposite of narcissistic personality disorder is empathy.

From this determination, I am giving a theory that the cause of self-gaslighting might come from being too empathy. The ability to sympathize with people and their perspectives make them easily understand and forgive people's actions. This makes them think that there's nothing wrong with the other person so they start to think themselves as the problem.

People who gaslight others may have mental health disorders, such as narcissistic personality disorder (NPD) or borderline personality disorder (BPD). They use this type of emotional abuse to exert power over others in order to manipulate people.