Why are we insecure ?

I walked into spanished classes legit annoyed as hell. Why? Because my Spanish teacher is super nice older lady but not at the same time. She can be very nice but when you hit her slight nerve she goes all wild. Thursday  a sub came into because she had a meeting. This sub was a very quiet young man,  maybe early 40s. I am writing about him because I saw how insecure he was and I didn't say anything to help. He constantly scratching his arm looking down, kept figiting with his hair and kept looking at him self in his phone. I wanted to tell him he looked good but okay or don't worry about how you look but in a nice meaningful way. I understand the feeling of caring what you look like and feeling ugly in your own body.... but I didn't say anything .....