In a footnote, Dostoevsky asserts that while the diary and the narrator are imaginary, such a person as the narrator not only exists, but that he must exist because he represents many people who are forced by the circumstances of society to live, as he does, underground.
Dostoevsky's footnote makes it clear that the Underground Man is not an absolute anomaly, is not an exception, but that in such a strict, scientific society as that of the nineteenth century, such a man must exist or else society would become a single, collective, mechanical robot. He is not a "representative man" or an "active man" who consents to the scientific determinism being perpetrated in nineteenth-century society; instead, he is that important and significant holdout against a scientific acceptance of life. Therefore, in a purely scientific-oriented society, he represents the man of consciousness who refuses to accept and to yield to the discoveries of science. Consequently, we must assume that in a mechanistic society, such a person as the narrator must exist, metaphorically, underground; that is, contrary to the general trend of the rest of society.