People with big egos have a persona like a Norman castle. The castle can look regal and impressive, befitting if not a king, at least a duke. A Norman castle is extremely difficult to penetrate and gives the master an air of invulnerability. If some local, unhappy with the taxes imposed by the Duke, wanted to take matters into their own hands, it would be near impossible for him to do anything.
People with massive egos act with similar confidence and appear invulnerable. The facade of their personalities can seem imposing and make the onlooker feel very small and insignificant.
Yet the very fact that the castle exists at all, just like the overbearing personality, is a mighty clue. Norman castles were built for a purpose. So, I would suggest, are massive egos. They are strategies of domination that are effective. Still, these strategies give away the fears of those they were designed for.
To notice that fear is the primary motivation, should be encouragement for people on the outside looking in.