Incest barrier is an ego defense mechanism against incestuous desires. This psychoanalytic concept attributes such mechanism to the internalization of social standards. This is explained as one of the possible reasons why some people cannot have normal sexual relationships with their partners whom they love but can have one night stands with strangers. Their incest barriers during childhood could have resurfaced in adulthood. It is theorized that this is caused by an excessive attachment to the opposite sex parent.