Your favourite mental muscle often dominates your personality (in fact, the technical term for it is: the "dominant" function). So, as it tends to dominate your personality, whether you use it in the inner or the outer world also has a big impact on your behaviour - and some of the differences between Es and Is are listed on this slide. When a mental muscle is "dominant", it is the 'boss' of your personality.

Bad Joke: The only male who is "boss" of the family is under three years of age.