Albert Camus, the novelist and philosopher compared the meaninglessness of the human condition to the Greek myth of Sisyphus:

Sparknotes:

Sisyphus was punished for all eternity to roll a rock up a mountain only to have it roll back down to the bottom when he reaches the top. Camus claims that his punishment is representative of the human condition: Sisyphus must struggle perpetually and without hope of success.

Wikipedia:

Camus presents Sisyphus's ceaseless and pointless toil as a metaphor for modern lives spent working at futile jobs in factories and offices. "The workman of today works every day in his life at the same tasks, and this fate is no less absurd. But it is tragic only at the rare moments when it becomes conscious."

1000 Words Philosophy:

Camus observes that a person’s life can become, essentially, a mundane routine: “Rising, streetcar, four hours in the office or the factory, meal, streetcar, four hours of work, meal, sleep, and Monday Tuesday Wednesday Thursday Friday Saturday and Sunday according to the same rhythm…”

I find life as futile and repetitive, in a philosophical sense, as Sisyphus's task to roll his rock up the mountain.

Futile as in, there's no real success condition.

Repetitive as in, we all toil at the same tasks: university, work, marriage, parenthood, retirement, and death. We can shake it up and (a) start a company, (b) move to Thailand, (c) do drugs, or (d) all of the above, but ultimately we all share the same human experience.

But Camus has a solution:

So long as [man] accepts that there is nothing more to life than this absurd struggle, then he can find happiness in it, says Camus.

Sisyphus can be happy if he accepts the futility/repetitiveness of his condition and smiles anyways.

This seems a bit weak to me right now LOL but I was satisfied by it earlier this week. In any case, Camus rejects other sources of meanings as at best intellectual leaps of faith.

Read more here: https://1000wordphilosophy.com/2019/05/01/camus-on-the-absurd-the-myth-of-sisyphus/