Why did Camus call suicide the only serious philosophical question?

Because for him, philosophy came down to one test: if life has no built-in meaning, does realizing that require ending it? Albert Camus wrote that there is only one really serious philosophical question, and that is suicide. He meant it as a question to be answered, not a recommendation, and his answer in The Myth of Sisyphus was no: the realization of the absurd, he argued, does not justify suicide, and instead requires 'revolt'.

Camus called this clash the absurd: the human need to find meaning running into a universe that answers with what he called 'unreasonable silence'. It isn't that life contains some particular tragedy; it's the mismatch between our hunger for answers and a world that offers none. He began The Myth of Sisyphus in 1940, during the Fall of France, when millions of refugees fled the advancing German armies, and published it in 1942, exploring how a person should live once they accept that mismatch.

Besides suicide, he also rejected the leap into religious faith, which he called a kind of 'philosophical suicide' because it abandons reason in favor of religious or metaphysical hope rather than facing the silence directly. What he proposed instead was revolt: living fully aware of the absurd, without pretending it isn't there and without fleeing from it.

To make the idea concrete, Camus turned to the Greek myth of Sisyphus, a man condemned to push a boulder up a mountain forever, watching it roll back down each time he nears the top. It's the perfect picture of meaningless, repetitive labor. Yet Camus ends the essay by insisting that the struggle itself can fill a person's heart, closing with one of philosophy's most quoted lines: one must imagine Sisyphus happy.