The Underground Man maintains that there is even some type of enjoyment in a toothache. For example, why does a person moan with a toothache? If he did not find enjoyment in moaning, he would not moan. First of all, the moaning represents the intellect's inability to understand the aimlessness of pain. But as the ache continues for days, the moans become a desire to force others to suffer as you are suffering and the moans become "nasty, disgustingly malignant." Also, he knows that the audience for whom he is moaning only loathes him for his efforts, and from these recognitions comes a perverse pleasure. He wonders if, ultimately, a man of acute consciousness and perception can ever respect himself.
Scientific rationalism, according to Dostoevsky, tries to categorize everything, place everything into its proper slot. Yet the Underground Man, in using the idea of the toothache, illustrates the fallacy of such attempts. When his imaginary audience ridicules him by laughing, saying "you will be finding enjoyment in a toothache next," the Underground Man develops this idea so as to show that science cannot predict a human being's reaction to pain or to anything else. Since all people universally agree that a toothache is unenjoyable, the Underground Man shows how the pain can be enjoyable, how the person enduring the pain enjoys wallowing in his own misery. This again points to the Underground Man's theory of man's contradictory nature, a nature which prevents him from fitting into the scientific mold which the rationalists have fashioned for him.
The idea of a man's moaning over a toothache carries also metaphysical implications. The moans are a protest against the futility and aimlessness of pain. The stupid person, or the man of direct action, simply accepts pain as a part of the everyday aspect of living, but the man of acute consciousness searches for some reason or some purpose to the pain. He moans at his inability to comprehend any valid purpose for his being inflicted with pain. The more the pain continues, the more fully he recognizes the discrepancy between enduring pain and the capricious inflicting of pain upon him. His increased moans, hopefully, will force others to see the absurdity of pain and man's inability to cope with it.
The Underground Man, having come to his realization about the aimlessness of pain, and having forced others to despise him because of his moans, then asks: can a man of acute consciousness (acute perception) ever respect himself? In other words, if the introspective man of self-consciousness constantly analyzes himself and his functions, he understands himself so thoroughly that it is impossible to respect himself. But, as he will later point out, few people have the courage to analyze themselves in any depth.
The idea of the function of pain and more particularly of innocent suffering receives Dostoevsky's fullest treatment in his later novels. For example, Ivan Karamazov investigates the idea that pain and suffering might have a function in God's total purpose for the universe, but since God didn't give us an intelligence sufficiently complex to understand it, he rejects the idea that the innocent must suffer and questions God's justice.
With these ideas about the pleasure in pain, we could wonder if the Underground Man finds pleasure in writing these Notes from Underground and, especially in the second part, if he receives pleasure from intentionally inflicting mental pain upon the prostitute, Liza?