From Sarah Bakewell in How to Live: Or A Life of Montaigne in One Question and Twenty Attempts at an Answer:
As Seneca put it, life does not pause to remind you that it is running out:
The only one who can keep you mindful of this is you: It will cause no commotion to remind you of its swiftness, but glide on quietly … What will be the outcome? You have been preoccupied while life hastens on. Meanwhile death will arrive, and you have no choice in making yourself available for that.
If you fail to grasp life, it will elude you. If you do grasp it, it will elude you anyway. So you must follow it - and "you must drink quickly as though from a rapid stream that will not always flow."
The trick is to maintain a kind of naive amazement at each instant of experience - but, as Montaigne learned, one of the best techniques for doing this is to write about everything. Simply describing an object on your table, or the view from your window, opens your eyes to how marvelous such ordinary things are. To look inside yourself is to open up an even more fantastical realm. The philosopher Maurice Merleau-Ponty called Montaigne a writer who put "a consciousness astonished at itself at the core of human existence." More recently, the critic Colin Burrow has remarked that astonishment, together with Montaigne's other key quality, fluidity, are what philosophy should be, but rarely has been, in the Western tradition.
As Montaigne got older, his desire to pay astounded attention to life did not decline; it intensified. By the end of the long process of writing the Essays, he had almost perfected the trick. Knowing that the life that remained to him could not be of great length, he said, "I try to increase it in weight, I try to arrest the speed of its flight by the speed with which I grasp it … The shorter my possession of life, the deeper and fuller I must make it." He discovered a sort of strolling meditation technique:
When I walk alone in the beautiful orchard, if my thoughts have been dwelling on extraneous incidents for some part of the time, for some other part I bring them back to the walk, to the orchard, to the sweetness of this solitude, and to me.
At moments like these, he seems to have achieved an almost Zen-like discipline; an ability to just be.
When I dance, I dance; when I sleep, I sleep.
It sounds so simple, put like this, but nothing is harder to do. This is why Zen masters spend a lifetime, or several lifetimes, learning it. Even then, according to traditional stories, they often manage it only after their teacher hits them with a big stick--the keisaku, used to remind meditators to pay full attention. Montaigne managed it after one fairly short lifetime, partly because he spent so much of that lifetime scribbling on paper with a very small stick.
In writing about his experience as if he were a river, he started a literary tradition of close inward observation that is now so familiar that it is hard to remember that it is a tradition. Life just seems to be like that, and observing the play of inner states is the writer's job. Yet this was not a common notion before Montaigne, and his peculiarly restless, free-form way of doing it was entirely unknown. In inventing it, and thus attempting a second answer to the question of how to live--"pay attention"--Montaigne escaped his crisis and even turned that crisis to his advantage.
Both "Don't worry about death" and "Pay attention" were answers to a midlife loss of direction: they emerged from the experience of a man who had lived long enough to make errors and false starts. Yet they also marked a beginning, bringing about the birth of his new essay-writing self.