When he started working on what would become “Oh, the Places You’ll Go!” Theodor Geisel — better known as Dr. Seuss —probably understood that it was his last book.

It’s unlikely that the beloved author knew it would become his most successful one, too.

Thirty years after its initial publication, the book is a perennial best-seller, a nostalgia-fueled, go-to gift at graduation time. More than 800,000 copies sell every year. Parents who received it when they finished high school are sending their own kids off to college with it now.

This year, the internet is already dotted with videos of celebrities and others reading the book out loud for housebound seniors, whose pomp and circumstance have been interrupted by the COVID-19 pandemic. Their futures, too: High school grads may start college in the fall still at home, with online instruction; those leaving college face diminished job prospects.

So there’s a different resonance to the book for the Coronavirus Class of 2020. It’s not just a feel-good story that steers the reader toward a rewarding life. It also points out that the journey is often marked by “Bang-ups and Hang-ups,” by lurches, stumbles and slumps. By being alone.

“Think about the two-page spread in the book of the Waiting Place,” said Philip Nel, an English professor and Seuss scholar at Kansas State University. “We’re all in the Waiting Place right now — waiting for the virus to pass, waiting for a vaccine to be developed, waiting to go back to our lives. Waiting.”

The unnamed boy in the story is told by the narrator that “somehow you’ll escape all that waiting and staying,” and that’s a worthwhile message in these troubled times, according to Susan Brandt, president of San Diego-based Dr. Seuss Enterprises, which licenses the use of the late author’s stories and characters.

“This pandemic is getting hard on people,” she said. “I think the book’s recognition that life doesn’t always go the way we want it to, that we have to face it ourselves and if we do there are people who will help us — that just feels really relevant today.”

Geisel was 84 when he started working on the story, in 1988. He was in pain from cancer-related surgeries to his neck and jaw. And he had decided he was through with doctors.

But he wasn’t downbeat about what would be his 48th book. He’d recently marked the 50th anniversary of his first one, “And to Think That I Saw It on Mulberry Street” and the 30th anniversary of perhaps his most famous one, “The Cat in the Hat.”

He zeroed in on a project that would speak to what he later called “limitless horizons and hope.” He spent months writing and drawing the story.

It opens with this:

Congratulations!

Today is your day.

You’re off to Great Places!

You’re off and away!

A boy dressed in yellow and wearing a stocking cap wanders through a distinctly Seussian world of wildly tilting buildings and mildly bemused animals, some of which echo the architecture and creatures of his earlier works.

The narrator tells him, “You cansteer yourself any direction you choose,” but also warns to expect being sent “up many a frightening creek.”

And will you succeed?

Yes! You will, indeed!

(98 and 3/4% guaranteed.)

Whenever he finished a book, Geisel liked to present it in person to his publisher. He would read the story out loud to a handful of people in a conference room. Using a color chart made just for him, he would work with the art staff to pick just the right hues for the drawings.

This time, he was too sick. He asked his art director, Cathy Goldsmith, to come to his house. “The book was extraordinary, but also a little bit sad,” she said. “I think he knew he was writing a farewell book. He was summing up.”

When the book came out in 1990, the critical reaction was mixed. One reviewer dismissed it as a “yuppie dream” that would appeal only to 30-somethings with highly paid jobs who feel “insecure because of the way things are going in the world.” Another critic applauded “the depth and levity that seem likely to make it one of everyone’s favorites. It also has the greatest thematic breadth of any book in the entire extraordinary Seuss canon.”

Readers delivered their own verdict. “Oh, the Places You’ll Go!” quickly rose to the top of the New York Times Best Sellers list — not the children’s book list, but the one for adult fiction.

When Geisel died on Sept. 24, 1991, at age 87, the book was still on the list. And it’s been returning there regularly during graduation season. It’s sold more than 15 million copies in all, Brandt said, and is now “the No. 1 selling Dr. Seuss book.”

Geisel was a writer who trafficked in pithy observations — “A person’s a person, no matter how small,” for example, from “Horton Hears a Who!” — and to Nel, “Oh, the Places You’ll Go!” is the culmination of that.

“I think he meant it for all of us,” Geisel said. “It’s his farewell, his salute, his last bit of wisdom — and not just for children. For everyone.”