Hamlet is still wondering why he has been procrastinating about doing what he knows is his duty, which is to assassinate Claudius and avenge his father's murder. Shakespeare seems to be taking great pains to emphasize that this is the main problem of the play, but he does not offer any definite answer. Therefore, critics have been speculating and debating for centuries about the so-called Hamlet Problem. The fact that Hamlet ends his soliloquy in Act 4, Scene 4 with the words, "O, from this time forth, / My thoughts be bloody, or be nothing worth!" is not convincing. He may have another opportunity to kill Claudius, as he had when he found the King alone and praying, and he may find some reason or reasons for failing to act. Characteristically, he only acts impulsively, when he doesn't have time to think. But thinking is his normal mode. It has been reinforced by many years of deep, solitary study at Wittenberg.
Samuel Taylor Coleridge writes in his "Hamlet Essay":
Hence we see a great, an almost enormous, intellectual activity, and a proportionate aversion to real action, consequent upon it, with all its symptoms and accompanying qualities.
Carl Jung, the famous psychiatrist and colleague of Sigmund Freud, identified two psychological modes or "attitudes," for which he coined the terms introversion and extraversion, and four conscious "functions," which are thinking, intuition, sensation and feeling. Hamlet is quite obviously an introvert, and the conscious function he favors (as Coleridge would agree) is thinking. Jung states repeatedly in his book Psychological Typesthat thinking requires the suppression of feeling, just as feeling requires the suppression of thinking. Killing Claudius--or killing anybody--would require a feeling of rage, and Hamlet cannot feel that rage if he begins to think along the lines that are represented by all his compulssive and convoluted soliloquies.