I came across the phrase "the feeling of unworthiness" in a Vipassana meditation book I'd picked up at a used bookstore. I've forgotten the name, but the phrase gave me a new way to see things.
Once I had it, I started noticing how much of what people do runs on it. So many of us are quietly trying to please someone — family, friends, our own idea of who we should be — because somewhere underneath we feel we aren't worthy of love or acceptance. It's a deep sanskara, conditioning that sits below thought. It's what makes a person spend years trying to prove something to their parents. It's why we put on masks to look good, why we play characters and add so much drama to the world instead of just being ourselves. It feeds anxiety, and it pushes people to great lengths to prove a point that never needed proving.