Esteem v. Reality
One’s opinion of themselves is not always an accurate guide to reality. One person may hold themselves in high self-esteem but others may not have such a high opinion of them. At the same time, some people with low self-esteem may be totally under-valuing themselves.
The solution? Get a reality check. Ask for feedback from others (formally and informally). Be open to hear it (not all feedback will be pleasant). Be willing to listen. Be willing to change.