It may come as a surprise to some people who mostly know me from conference speaking, but I'm an extreme introvert.
I actually love public speaking and can't remember a time I ever feared it. I'm also, in most situations, hardly what would be described as shy.
But Cain makes clear that those two things are completely consistent with (and are largely orthogonal to) being an introvert.
My introversion mostly manifests in the fact I get most of my energy, enjoyment, motivation and excitement from being alone.
I don't mind spending time with people, I just don't need much of it. I need time alone, though.
I love spending timing with friends and family, especially over a nice dinner. But I need time alone afterwards to recharge and "do my own thing".