To understand what it is that makes us introvert’s tick (and run away screaming from extraverts), we need to look at what goes on inside the introvert’s mind.

Introverts are more easily stimulated by external stimuli than extraverts.  This isn’t just about people, talking, or loud noises – this is about everything.  If you put a drop of lemon juice on 100 people’s tongues, and measure how much saliva is produced – those people producing the most will be introverts.  Even the stimuli of lemon juice on the tongue stimulates an introvert more than an extravert.

We can see it in babies too.  Some babies are placid and content, whereas others are easily agitated – scared by almost everything around them.  Those louder, more agitated babies are the ones most likely to grow up to be introverted.  The reason is the same – it seems they are more stimulated by the environment than their extraverted brethren, and react more strongly to it.

So if babies predict our introversion, it it something we are born with, an inescapable fate of genetics?  The answer is a definite maybe.  Studies on twins have shown that about half our chance of being introverted in inherited from our parents, whereas the other half comes from our environment growing up.  It would seem that we inherit not introversion, but a proclivity towards it, and that even a child born from an extraverted line may, in the right circumstances, discover their inner introvert as they grow up.

The stimuli most introverts face is fear.  Thats your essential reaction to whenever something happens that you don’t expect.  Fear.  Slight fear, perhaps, but enough to make you slightly weary, slightly startled.  This can be when a car passes you on the street, when a stranger talks to you, when you hear an unfamiliar piece of music.  The introvert’s mind has a fear reaction.

The brain of an introvert’s job is then to manage this fear.  We don’t all go along each day jumping out of our skin at each and every thing that happens to us (though, I’m sure the most introverted amongst us – myself included – have days when everything that happens just seems to be too much, and we would really rather roll up into a ball and hope the world goes away).  Its the job of the brain to make oll of this bearable – to take away these negative responses and manage them.

The brain does this by learning – the more familiar he situation, the more times the brain has handled similar experiences without suffering, the more we are able to let them pass.  In effect it uses a low level of something akin to will power to tell the initial reaction -albeit subconsciously - “Thanks but no thanks”.  But even this is slightly tiring.

Moreover, we still experience lots of unknowns in our lives.

Take social interactions, for example – they are inherently unpredictable.  People have a habit of doing different things each time you meet them.  They’re annoying like that.  So people are setting our fear alert’s buzzing, and its our brain’s job to quieten itself down again.  Now some introverts – those who have had a lot of social experience – may do a good job of drowning out the buzzer.  but others – especially those who may have had less pleasant social experiences in their youth, may not drown the buzzer down quite as much.  And will begin to consciously find the more difficult of social situations (meeting new people, for example) actively unpleasant.  This then takes active willpower to get through.  And these introverts are drained of energy far faster.

This is why introverts (who still crave some human interaction), tend to have smaller groups of friends – and closer friends.  Introverts build up strong bonds of trust which underly their social interactions to make them far less of a drain and allow them to enjoy the socialising part more.

But there is more to an introvert than this.  The introvert, knowing the difficulty of interacting with other people learns techniques to manage this.  Specifically the introvert learns a method to avoid frequent failure: Abstract Thought.  Fearing rejection – or whatever sort of pain the introvert has learned to associate with the fundamental fear their fear buzzer raises in them – the introvert becomes a planning machine.  When thoughts arise in the introvert’s mind, the introvert examines them, and looks them over, seeing if any of the thoughts may have particular merit, examining any flaws in their actions.  Only having looked at a thought from all sides does the introvert feel happy with it – does it become particularly real to him.  At this point, the introvert is willing to express his thought to others.

This leads to problems socially.  In conversations, introverts will often have to hold back as they fully absorb and take in the ideas that other people are throwing about.  To the extravert, it might look like the introvert is not playing his part, is sitting on the sidelines – perhaps not even understanding what is going on.  Either way, the introvert may appear arrogant, rude or stupid.  However, in the introvert’s mind, he is engaging fully.  Not with the people, but with the ideas.  Give an introvert time, and, when he has finished incubating them, the ideas he comes up with are likely to be fully formed and ready to be used.

Throughout this book, I have made the assumption that extraverts don’t realise that introverts are different and think in a whole different way from them – but from talking to introverts, I find that introverts also don’t understand the difference in how extraverts interact with the world.