Knowing this, I think it's pretty obvious introverts can learn and appear as extroverts, but eventually they hit a point where they have to say "bye" and be alone doing nothing productive for a while.
As an anecdotal data point, I was very introvert and I did learn to "be extrovert" and many people wouldn't notice at all, but at the end of the day I need to be alone, sometimes for days to recover and be productive again.
Even though it's anecdotal I think we can't generalize and say "introversion doesn't exist". There's a lot of factors involved. Stuff may be even more complex when dealing with an ASD.
Perhaps, I might lie in that "unhappy everywhere" group... but I think I was pretty happy in college around the bunch of other like-minded friends. It's just that those happiness activity metrics might not best match with society's generally accepted metrics. But now that I am more aligned to general things "happy" people do, I usually find myself more aloof and unhappy along with usually tired feeling with all the "extroversion". Have practiced enough for years (especially being a founder of a company now), but it's still pretty tiring :(
Also mostly the happiness experienced in such situations is often temporary and bonds formed are feeble, as I can't keep up the "extroversion" for too long and soon become boring for a lot of people, so I am actually trying to move away from that now :)
I would rather people experience me as "elsewhere" than "boring" and I especially dislike when I internalize others' perception and start seeing myself as boring, too.
It's all so complicated.
Anyway, it's a topic that interests me a lot, so feel free to connect (twitter, email in my profile) if you want to chat about it.
He accuses people of misunderstanding the terms "introversion" and "extroversion" but does the same thing himself by associating them with the stereotypical behavior that we commonly think of rather than the underlying neurological differences. Those differences are real (dopamine vs acetylcholine, different blood flow patterns in the brain) and appear to be linked to genetics [1] [2]. Yes, the terminology both in common use and within Psychology is imprecise and often misapplied, but that doesn't mean that there aren't actual differences.
He dismisses the "energy" interpretation as a simple matter of fatigue from undeveloped skills. I haven't seen any research that supports that or indicates that individuals can change their fundamental reaction to external/internal stimulus through practice and effort. Ie, an introvert can learn to work a crowd and present as an extrovert, but afterwards they will be exhausted compared to a true extrovert.
I do agree that the positive external traits that we typically associate with each (sociability, friendliness, assertiveness vs ability to focus on solo tasks without becoming bored) are enabled by skills that anyone can learn no matter where they are on the introversion/extroversion spectrum and people shouldn't give up just because they find it hard. But an introvert will have a fundamentally harder time developing the social skills and will need to recuperate afterwards (and same for an extrovert with solo skills). I don't think it's productive or helpful to encourage the "just toughen up, buttercup" dismissive approach.
1: http://www.sciencedirect.com/science/article/pii/S0926641005... 2: http://www.jneurosci.org/content/32/50/18087.short
TL;DR most people think of introvert/extrovert on one dimension, but in fact some people are both (happy alone, happy in groups) and others are neither (unhappy alone, unhappy in groups). So it makes more sense to think of it as two dimensions (some nice charts in article to visualise this).
Since reading this article I've tried to become more "extrovertable".
Not for everyone - for many it might be best to focus on a single dimension, but it's helped me thinking about it in 2 dimensions and explicitly practicing becoming better at both "skills".
[0] https://www.inc.com/joshua-spodek/there-are-no-such-things-a...