seneca

It is inevitable that life will be not just very short but very miserable for those who acquire by great toil what they must keep by greater toil. They achieve what they want laboriously; they possess what they have achieved anxiously; and meanwhile they take no account of time that will never more return. New preoccupations take the place of the old, hope excites more hope and ambition more ambition. They do not look for an end to their misery, but simply change the reason for it.

...Putting things off is the biggest waste of life: it snatches away each day as it comes, and denies us the present by promising the future. The greatest obstacle to living is expectancy, which hangs upon tomorrow and loses today. You are arranging what lies in Fortune’s control, and abandoning what lies in yours. What are you looking at? To what goal are you straining? The whole future lies in uncertainty: live immediately.

— Seneca, On the Shortness of Life