What can be the reason behind lack of self confidence in any person?

Negligent parents. Having parents that weren’t there when you needed support.
Disapproving parents. Never getting positive feedback as a child can leave you chasing approval from others.
Physical insecurities. Not being able to fulfill society’s standards of what’s ‘good’.
Past trauma. A person who was abused might believe they deserved it and that is detrimental to their self-worth.
Anxiety and depression. These issues can hinder most areas of your life, and self-confidence is one of them.
Bad friends. Having friends who are fake and manipulative.
Negative self-talk. At some point, they developed this pattern and now it runs them.
Comparing themselves. People tend to compare their chapter 2 with someone’s chapter 57. It’s irrational.