13 Things Mentally Strong People Don't Do: Take Back Your Power, Embrace Change, Face Your Fears, and Train Your Brain for Happiness and Success

by Amy Morin

Resentment of others’ success is also a result of deep-rooted insecurities. It’s hard to be happy about a friend’s accomplishments when you feel bad about yourself. When you’re insecure, someone else’s success will seem to magnify your shortcomings.