Whether due to a lack of self-awareness, fear, self-denial, self-preservation, shame, or some other non-malicious driving force -  the person is not able to see, acknowledge or accept that their actions, thoughts, beliefs and words are not in alignment and that what they are saying is likely contradicting reality. They are lacking integrity. And when they refuse to acknowledge this, especially on a continuous basis, they are gaslighting you. Whether they mean to or not.