This pair of wonderful diagrams has been circulating around the internet without source or acknowledgement – but as far as I can see the original designers are here, and we should acknowledge their brilliance.
Jung’s original conception, introversion is a focus on the inner contents of one’s mind, and extraversion is a focus on external objects and the outside world. So extraverts get energy from other people, and introverts get energy from thinking. It isn’t that introverts don’t like other people or don’t know how to deal with them: it’s that they find them draining of energy (though not quite in the sense of this Dilbert cartoon). Introverts can be very socially skilled, though they’re unlikely ever to shine in a field such as telesales. It’s rare to find an extrovert with poor social skills (though they do exist), but it’s common to find extroverts who prefer to do their thinking by talking to other people.
The second reason these diagrams why these diagrams are great is that they’re actually useful. Most discussions of extraversion and introversion in pop psychology or HR literature focus on “finding your type” or working out where you are on the introversion-extraversion spectrum, but don't tell you what to do about it - except, usually, to imply that if you're an introvert you shouldn't be promoted into management or do any kind of job which involves working with people. (Hence the need for ripostes, such as Susan Cain's Quiet.) These diagrams address the problem that if you're an extrovert you probably don't know how extroverts like to be treated (and they're unlikely to tell you), and if you're an introvert you may know what extraverts like but don't have the confidence to do it for them. These are diagrams which offer the possibility of a better world.
And the third reason why these diagrams are great is of course that they're superb pieces of design. Pithy and memorable text, engagingly laid out. (I think the variation in type sizes forces one subconsciously to slow down and pay more attention while reading the text, hence encouraging one to pay attention to what it actually says.) Writers and designers of motivational aphorisms, take note.