Answer:
Insecurity? If there's one person who about insecurity, its me. I spent my early childhood incredibly insecure. And up until now, I still know lots of other people who are stuck in that STAGE. There are soo many causes of insecurity that they all cant be named. When a person is insecure, it technically means that they have no belief in themselves. In other words, they dont love themselves (thats mostly the case) so if you think about situations where a person's morale goes down, it can be considered as a cause of insecurity. For example, bullying, insulting comments, particularly things that make you feel bad about yourself.
Hope that answered your question! :)