What's the usual quality shown that someone is extroverted/introverted or has a dominant E/I element?

Mostly I see from definitions:

high energy/low energy

and I also see

objects/fields (things observed apart from the observer/things perceived through the observer by means of feelings)

some people say Xi is more of a system and Xe is more of a method

or Xi is more method oriented and Xe is more goal oriented

sure every element has its own description that we have knowledge about, but what's with the Xi or Xe, and why are people introverts or extroverts?

so what is really the best way to define this dichotomy or the difference in elements of I/E?