1. the person can lash out at other people as a product of their own issues
2. it can cause the person to be envious and grow a sort of vendetta against those who are happy with themselves
3. low self esteem can lead to depression, or the person trying "fix" themselves rhrough unhealthy methods
4. the person can feel unworthy of happiness or being treated fairly, thus allowing people to treat them badly and even be drawn in by people who treat them badly.