There’s an interesting, half-elliptical sentence in Book 11 of Marcus Aurelius’s Meditations. “Think of the hill-dwelling mouse and the house mouse,” he writes, “and the agitation and trepidation of the latter.” Some readers will have no idea what that means. But those familiar with the classics will recognize it immediately.

Two thousand years ago, Marcus was summarizing to himself a lesson from Aesop’s then some 800-year-old fable about two mice from different environments and what they learned spending a weekend in each other’s worlds. Marcus happens to be relating to the country mouse, drawing from the fable the serenity and peace of a quieter life away from Rome.

But the impressive thing here is that, even as the most powerful man in the world, Marcus was still returning to lessons from his youth.

This is precisely why we must continue to return to such lessons ourselves. Notice, Marcus is not referencing silly stories from childhood. In part, because that genre didn’t really exist, but also because that wasn’t what Roman education focused on. Students were taught fables and read moral biographies for the purpose of raising well-adjusted adults. Entertainment was fine—and Aesop is very entertaining—but the ancients wanted to impart real wisdom, too.

The time we have each day, the books we choose to read, the content we consume—this is some of the most valuable territory in our lives. What will we use it for? What will we fill our heads with? What will we expose ourselves to?

It must be, as the ancients understood, stories of heroes and lessons, wisdom and insights. Not because such material is sophisticated or impressive, but because we will need it. Marcus needed Aesop in the palace. Seneca needed his philosophers in exile. We will need ours, too—in moments we cannot yet predict.

Return to the lessons. They’re waiting for you.