Final answer:
Thoughts reflecting a belief that life has no purpose or meaning, and that actions hold no significance, represent nihilism, a philosophical view that is skeptical of meaning, truth, and value.
Step-by-step explanation:
Thoughts such as: "Life has no purpose or meaning," "Truth cannot be known," and "What I do doesn't matter" best typify the philosophical position known as nihilism. Nihilism is characterized by a deep skepticism towards notions of meaning, truth, and significance in life, asserting that these concepts have no innate value or are unobtainable. This contrasts starkly with egoism, which prioritizes self-interest; hedonism, which equates the good with pleasure and the avoidance of pain; and altruism, which involves the selfless care for the well-being of others.