It depends on how you define ghosts. For instance, if you define them as independent of our minds, with their own free will and “substance”, that would be a tall order. But, if you define them as relics of our own mind, comprising of the sum total of our perceptions, fears, needs, wishes, etc., well, yes that kind of ghost exists in all, if not most, of us. Occasionally they are even visible, especially if you suffer from schizophrenia.