Some of us learn this as young teens. Some learn it in early adult hood. Others make it to mid 30's and mid 40's and still haven't gotten off of mommy's tit.
Insecurity within yourself shows BRIGHTLY to the outside world. Every one around you sees your insecurity, even if they don't say anything. True friends and those that love you tell you the truth. They tell you what's really going on. When you argue against that or fight against that and act all macho or pig headed, your insecurities just show through even more. What you need to do is take a cold, hard look at yourself, within yourself, and see how you really are. Take that and actually grow up. Life will never be a cake walk, but it does get much smoother when you take an honest look at yourself and STICK WITH THAT.
It's called growing up, and it's a hard thing to do. And gets even harder the older we get. So start now, before even more life passes you by.