Insecurity

For many it's a big let down and for many it's a tool to bring someone down. We are not born with it, this just pop up with the passage of time and conditions. 98% of the humans on the surface of earth are insecure about their looks, 90% are insecure about their partner, 82% are insecure about their job, 73% are insecure about their own sexuality, and the list goes on. It is humanly impossible to find one person who is self-secure or rather the words should be confident about life, sexuality and other stuff. Everyone is and will be insecure about something or the other that is not in our own hands. My basic question is why people get insecure? What is the main cause of the insecurity? Can it be cured? 

The answer to all these questions are not as simple as one may think. One may say that the insecurity related to ones image or looks can be handled by going through the instant makeover or attending personality development classes. But can that same person answer one simple question, if that could have helped then why there are too many cases where people just adapt to the change they are suggested or molded in and forget the real them?