It was Jung who coined the terms. And what he meant by them, as I interpret it, is that introversion refers to preoccupation with what’s inside one’s mind (memories, imagination, thoughts, etc) and extraversion refers to preoccupation with what’s outside of one’s mind (sensations, body movements, etc.)
Thus, an extreme introvert would be someone who is completely oriented towards what’s inside one’s mind i.e. a man who, literally or figuratively, has no body and who has no experience with the external world; similarly, an extreme extravert would be someone who is completely oriented towards what’s outside of one’s mind i.e. a man who, literally or figuratively, has no brain and who lives completely in the present.
An average introvert would be someone who spends less time experiencing the external world and more time thinking about it (e.g. building a model of it or figuring out the most efficient way to attain a goal given a model and a starting point.) Thus, an average introvert has short periods of interaction with the external world (observation and action) and long periods of reflection. An average extravert would be precisely the opposite – someone who has short periods of reflection and long periods of interaction with the world. (And ambiverts would be people who think as they act and act as they think.)
So it is not that extraverts do not think, it’s just that they spend less time thinking than some introverts. (Obviously, by definition alone, not all introverts are thinkers. To be an introvert simply means to spend most of one’s time inside one’s head – thinking isn’t the only process that can take place inside one’s head.)
Brainstorming sessions typically consist of people who, extraverted or not, think in an extraverted manner during those sessions i.e. who think for a very short period of time before coming up with an idea. The average generated idea is most likely to be of low quality but since there’s a lot of them the probability that at least one of them is of decent quality is high.
So my point that introverts spend more time “figuring out what’s right and what’s wrong” than extraverts do remains unaddressed.
By the way, notice that nothing about the definition of the words “introvert” prohibits introverts from exhibiting any degree of anger. In theory, an introvert can exhibit the highest degree of anger conceivable at every point during his life. And yet, even such an introvert would fail to qualify as a choleric. Why? Because the word “choleric” means more than “someone who is very angry”. It refers to specific kind of anger. It’s a specific expression of anger – exclusive to extraverts – that one can call “outwardly expressed anger” or quite simply “extraverted anger”. “Yellow bile” is related to this type of anger. “Black bile” (or “melan chole”) is related to inwardly expressed anger. Make a choleric become introverted and you get a melancholic.