The more you think how great you are the less you are. Or the more you think how great you are the greater you become. Which is it?

There is a certain way of thinking which believes that in order to gain confidence and have others respect you that you must first respect yourself, believe in yourself and the rightness of your decisions.  This is a very common way of thinking and there is a lot of support for it in many  popular psychologies.  This kind of "believe in yourself" strain, or aspects of it,  goes back at least to Emerson in terms of thinkers and possibly to older religious interpretations.  You never admit a mistake or to being wrong because once you do then others will not respect you at all.  You must keep up that veneer of rightness whatever you really believe.  I have heard this from many people in different situations and there are many people who pretty much live their lives by it.  Understand this and I think you will have a better chance of understanding Trump.  He doesn't really think he is "great" but he says that so that people will know he has confidence in himself - always positive, best-foot-forward, look-em-in-the-eye, act,  and don't flinch.