Why do we do anything if nothing lasts forever? Every action we make is but a blip on the finite timeline of the universe, ending with the heat death. All our actions fade into insignificance as they become the past. Similarly, on a smaller scale, why do we do things if life is finite too? What difference would it make to the individual who is unable to witness the effect of his actions?

I presume you're asking a philosophical question about the rational justification of our actions rather than simply a psychological question about our actual motivations for doing them. The first thing to emphasize is that your question isn't rhetorical (and I'm not saying that you meant it to be). In other words, the burden of proof rests with anyone who says "You're right: there really isn't a good reason to do anything if nothing lasts forever, if our every action is but a blip in the overall history of the universe." Whoever asserts the claim I just quoted owes us an argument for it, because it's very far from obviously true. I've seen arguments -- or at least what loosely resemble arguments -- for the quoted claim, but I've never found them persuasive, as I explain in this short magazine piece. A classic discussion of this issue appears in Thomas Nagel's 1971 article "The Absurd," available here.

So the reasons we typically give for our actions can't be dismissed in advance, and they'll depend on the specific action in question. Why listen to a splendid performance of a piece of great music? Because it's ennobling and deeply satisfying, even though the performance ends and even if the composition itself won't last forever. Why stop a small child from grabbing a pot on the stove and drenching himself with the boiling contents? The answer is too obvious to need saying. I've never seen a good reason to think that the answers to such questions automatically become inadequate on the assumption that nothing lasts forever.

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