Most of us are wary of the extremes. Extreme extroverts are as questionable as extreme introverts. In either case, we might ask, "What kind of drugs are you on?" For extreme athletes, we might attribute a death wish. Look up the word "extreme" on Google, and one of the related searches you'll see is "extreme couponing". Enough said.
It's easier to understand the common ground than it is to venture towards the edge.
Last year, I was asked how I know that I'm an "extreme introvert". I thought it was an interesting question. What makes my introversion extreme? And how do I know that's what I am? These are two very philosophical questions, but I'll try not to get too deep while answering them.
Part of the reason that I use the phrase is because more and more literature is finally being published about introversion, and the topic is described in an overly generic way. It's written about in such a manner as to include most of the world. Evidently, up to fifty percent of the population falls somewhere on the introversion spectrum, meaning half of us have at least some introverted tendencies. When you consider this, you can see why I -- among others -- would try to make a distinction. I classify myself as an "extreme" introvert because my introversion seems to be amplified. It's the difference between having mild tendencies versus being very clearly introverted. Simply put, the word introvert is overused; so I've added a modifier -- if introversion means "turning inwards", then extreme introversion means "turning inwards with gusto".
But how do I know that I'm on the deep end of the introversion spectrum? There's no exact formula for measuring these things -- it's guesswork, at best. There are tests online (e.g., the Meyers-Briggs test) that tell us how introverted we are, as a rough percentage, but the best test is experience. I know how I am in comparison to others because I spend time with people. I put myself in situations that allow me to make comparisons. I socialize now and then. You might say that I experiment.
How do I know? I know because I've tried being like everyone else, and I've also allowed myself to stop trying and to just be me. The difference is huge; in fact, the difference is extreme.