Shakespeare understood introversion and extraversion even without having the two terms in his vocabulary. In his portrayal of Brutus and Cassius in Julius Caesar he deliberately creates two contrasting but complementary characters. Brutus is an introvert who is often shown alone, either reading or meditating. Cassius is an extravert who operates through other men, measures himself against other men, and is never alone throughout the play.
Like many business partners and married couples, Brutus and Cassius complement each other. Cassius could not have brought about the assassination of Caesar without Brutus; Brutus would never have participated in the plot without Cassius’s passionate persuasion and covert machinations.
Partnerships between introverts and extraverts, like marriages, can function effectively, according to C. G. Jung, unless they are analyzed.
The introvert sees everything that is in any way valuable for him in the subject; the extravert sees it in the object. This dependence on the object seems to the introvert a mark of the greatest inferiority, while to the extravert the preoccupation with the subject seems nothing but infantile auto-eroticism. So it is not surprising that the two types often come into conflict. (Carl Jung, attributed to 1923 lecture.)
This is dramatized in the famous tent scene in Act 4 when the two generals have their acrimonious falling out.
In such a time as this it is not meet
That every nice offense should bear his comment.
Let me tell you, Cassius, you yourself
Are much condemned to have an itching palm,
To sell and mart your offices for gold
I did send to you
For certain sums of gold, which you denied me;
For I can raise no money by vile means.
By heaven, I had rather coin my heart
And drop my blood for drachmas than to wring
From the hard hands of peasants their vile trash
By any indirection.
The difference between the two characters is nowhere more glaring than in this argument. At one point Brutus says, “Away, slight man.” Their differences are irreconcilable. They demonstrate the truth of Jung’s statement: “This dependence on the object [in this case gold] seems to the introvert a mark of the greatest inferiority, while to the extravert the preoccupation with the subject seems nothing but infantile auto-eroticism.”