In Notes from the Underground, the isolated anti-hero lives under a strict, harsh philosophy of his own choosing. He is convinced of a series of certainties, such as the necessity of suffering. He needs to find real justifications for all actions, but he always fails to do so and thus can never act. His other doctrines include: Real men of intelligence can't ever become anything. Free will is man's most prized possession. The list goes on, as does the Underground Man's vehement adherence to these beliefs.
Although the Underground Man claims to be a romantic, he is really a hardheaded realist for whom nothing is sacred.