In this painting he can see a man carrying an enormous rock and trying to climb the mountain.

He is Sisyphus, the founder and the King of Corinth, who was intelligent and very rich and got his fortune not always by legal means. He cheated Thanatos, the God of Death, chaining him with his own chain. He also tricked Hades, the King of Death. Therefore he was condemned in Tartarus to an eternity of rolling a boulder uphill then watching it roll back down again.

It means that any effort to achieve unattainable things is useless and vain.

From my personal point of view, I don’t agree with that. Because if you try to get important goals perhaps you will never get all of them, but trying to achieve difficult projects is good for your personal growth.