In his book Psychological Types, C. G. Jung writes:
besides the most differentiated function [in our case, Hamlet’s thinking], another, less differentiated function of secondary importance is invariably present in consciousness and exerts a co-determining influence. [The other three conscious functions are intuition, sensation, and feeling.]
This seems to provide the best explanation of the so-called Hamlet problem: Why doesn’t Hamlet simply kill Claudius the first chance he gets? Hamlet, who is obviously an introvert, asks himself that question, notably in his soliloquy in Act 2, Scene 2, in which he berates himself for his failure to act. For example:
Why, what an ass am I! This is most brave,
That I, the son of a dear father murdered,
Prompted to my revenge by heaven and hell,
Must like a whore unpack my heart with words,
And fall a-cursing like a very drab,
Hamlet’s problem, to refer back to Jung, is that his thinking “must rigorously exclude feeling”—and without feeling murderous rage he cannot commit a murder. Whenever he does act decisively--as when he kills Polonius, when he boards the pirate ship, and when he grapples with Laertes in Ophelia’s grave—it is always before he has had a chance to think. When he finally kills Claudius it is when his normally repressed feelings have taken precedence over this introverted thoughtful nature.
…feeling can never act as the second function alongside thinking, because it is by its very nature too strongly opposed to thinking. Thinking, if it is to be real thinking and true to its own principle, must rigorously exclude feeling.
The reverse would be true of a person whose dominant conscious function was feeling. Feeling would rigorously exclude thinking. We have all known people of both types—those who appear unfeeling and those who appear unthinking. Laertes, who is generally accepted as Hamlet's foil, might be considered a feeling type as well as an extravert. He acts impetuously but is easily manipulated by King Claudius because his dominant feeling function excludes thinking.