I've suffered a lot with this in my life, its become part of my coaching to show people how it can become a governing factor in our lives without us even knowing it. It's a multifaceted belief system and absolutely I agree that it starts with complex childhood experiences that many of us could not have avoided or responded any differently. Something that helped me massively was understanding the influence of generational trauma. Many of my insecurities were mine, many were my mothers, and understanding her childhood in parallel to my own has really helped me understand those crippling negative beliefs. That pretty much echoes the other comments here but its a topic I could talk about for days lol.