I think part of it can be explained or attributed to a life of people "catering" to you. Higher social class will in a lot of circles mean that a lot of people

I think part of it can be explained or attributed to a life of people "catering" to you. Higher social class will in a lot of circles mean that a lot of people look up to you or wants to be your friend. One way of doing that is always giving the higher social status peer a lot of praise for anything he/she does. If you always receive a lot of praise for anything you do, no matter the actual significance of it, then naturally your own perception of your skills inflates unproportionally to reality.