Usually, someone develops low self-worth and lack of confidence in early childhood years. This could stem from being bullied, rejected, verbal/mentally abused, or repeated failures in a person's life. Not knowing who you are in Christ can impact your feelings of unworthiness.
How many times have you asked yourself, quietly or out loud What's wrong with me? Have other people ever said to you, What's wrong with you?, after you have failed to do something or live up to their expectations?