Think of a book that you’ve read that changed your life. How long ago was that? How long ago was it written?

Now think of all the things that have changed since that reading. In the world. In you. Perhaps even in our understanding of science or history or the biography of the person who wrote it.

All that is why you need to go pick up that book–indeed many books that have influenced you–and read them again. “Books remain the same,” the beloved writer Italo Calvino once said, “but we certainly have changed, and this later encounter is therefore completely new.” Or as that favorite poet of Marcus Aurelius, Heraclitus, said, “no man ever steps in the same river twice, for it is not the same river and he is not the same man.”

As we change and our contexts change, what we discover and get out of a book changes too. This is why Marcus was reading Epictetus when he was in line for the throne and when he was emperor. The book that he read at 25 was with him always, and each time he picked it up, it was different. This is why Stockdale was reading Epictetus when he was training to become a fighter pilot and why he returned to it after being released as a prisoner of war, even writing his own book about it, Courage Under Fire. This is why General Mattis carried Marcus Aurelius with him on every campaign. And this is why we too must return again and again to our favorite books and writers. You will benefit anew from every encounter.