Self-esteem is formed by an individual’s opinion about themselves, which describes their overall sense of self-worth or personal value. Self-esteem can involve an assortment of beliefs about the self, such as the assessment of one's own outlook, value system, emotions, and conducts. As we know, self-esteem is an important aspect of personal success and happiness.
On the high spectrum, too much self-esteem can lead to narcissism which can certainly be repulsive and possibly damage personal relationships.
On the low spectrum, it can leave the person feeling helpless and depressed, which leads to bad choices that falls into destructive relationships or failing to fulfil their full potential. Either way, self-esteem levels at the extreme high and low ends of the spectrum can be damaging, so the ideal is to strike a balance taking the mid-path, which is a realistic yet positive view of the self.