William Steig’s original 1990 picture book Shrek! has a few elements that Shrek fans will remember from the 2001 animated movie it inspired. There’s a big, green, lumbering protagonist with a prominent gut and weird little ear-antennae. (Eartennae?) He’s crude and ugly, but he’s extremely proud of the way he frightens and revolts people. And he does eventually meet a donkey, fight his way into a castle, and meet a princess whose face matches his own.

But the movie’s credited writing team — Road to El Dorado, Aladdin, and Pirates of the Caribbean team Ted Elliott and Terry Rossio, and TV veterans Joe Stillman and Roger S.H. Schulman — left out a lot more than they kept in. For instance, the original Shrek had parents, a similarly unlovely couple who begin Steig’s book by booting him out of their home so he can go have adventures of their own. (It’s a literal booting, but it’s pretty amiable: In Steig’s illustration, all three of them are smiling as Mom and Dad kick him through the air. Shrek looks like he’s going on an enjoyable thrill ride.)

Original Shrek smells so bad that trees lean away from him as he goes by, and he’s so ugly that he can cook food just by glaring at it, with an eye-laser effect that looks exactly like a colored-pencil version of Superman’s heat vision. Shrek also breathes fire and blows smoke out of his ears for fun. For him, being hideous isn’t just a lifestyle, it’s a literal superpower. Steig never describes him as an ogre in the book — he could just be an unusually repugnant human with mysterious eartennae, or he could represent his own unique species. (His parents are snaggle-toothed, patchy-haired critters with pastel skin, but they have normal ears.) Regardless, though, he’s definitely a monster.

It isn’t hard to figure out why the screenwriters scrapped all of that when they turned Shrek! into a movie. Shrek was a subversively rude, irreverent twist on fairy-tale movies that felt entirely fresh to audiences in a limited theatrical-animation era where Disney was putting out amiable comedies like The Emperor’s New Groove and A Goofy Movie, and competitors like DreamWorks and Pixar hadn’t yet fully forged their identities. But it’s still a relatively conventional story compared to a lot of the animated stories that followed. The protagonist is a monster, but he goes on a standard hero’s journey of self-discovery, acquires a sidekick, battles a dragon, and wins a princess. Steig’s original Shrek! is a much weirder story, one without significant conflict, and full of oddball details that go nowhere. In its original form, it was never suited for the screen.

And that’s because Steig had a unique storytelling sensibility that was often more about philosophy and observation than about action. A successful New Yorker cartoonist who famously didn’t start writing children’s books until he was 60, Steig scripted and illustrated some true children’s classics that don’t feel like anyone else’s books. Like Shrek!, his other children’s picture books sometimes feel arbitrary and chaotic. Like The Amazing Bone, in which a little girl-pig forms a close friendship with a talking bone that saves her life. Or Caleb & Kate, about an endlessly squabbling husband and wife who get separated when a witch practices her new spell on Caleb, turning him into a dog.

Or Sylvester and the Magic Pebble, about a donkey who finds a magic wishing-rock, and makes a terrible mistake with it. Like so many other children’s books, Steig’s often center on anthropomorphized animals and other non-human characters who often save themselves from danger through clever and inspired choices, sometimes learning lessons along the way. But just as often, his books are about predators and their victims, and about random bad luck that can only be mitigated by equally tremendous good luck.

That acceptance of the randomness of the universe, the reliance on coincidence as much as contrivance, can give his books an unusually unsettling quality — or make them more comforting than most kids’ fare, because they acknowledge that there are things we can’t prevent, and things we don’t fully understand, but have to live with nonetheless. Steig was as interested in states of mind and the road to acceptance as he was interested in action or adventure. One of his most action-oriented children’s novels, Dominic, follows an adventurous dog through a series of battles with a notorious bandit gang, but the dog Dominic spends as much of the book listening to other people’s life stories and attending a wedding as he spends fighting off the villains. In one lengthy subplot, he meets an ancient, ailing pig and spends days cooking and cleaning for him, and talking with him about life. When the pig eventually dies of old age, Dominic mourns, buries the pig, and spends a lonely night wistfully musing over his own mortality.

Another of Steig’s best, Abel’s Island, gets even more contemplative. When sophisticated aristocrat-mouse Abel is washed away from his wife during a horrific storm, he’s marooned alone on an island. Most of the book is simply about Abel building a solitary life for himself, learning to battle the elements and come to terms with his own loneliness — and again, his own mortality. It’s heady stuff for a children’s novel, but it stands out, for kids and adults alike, because it takes time to explore the mundane details most books whisk past, treating the monotony of daily work as if it’s just as important as any life-changing plot twist.

Shrek! the picture book isn’t as ruminative, and it certainly isn’t slow. Shrek has barely been kicked out of his house when he meets a witch and asks her to tell his fortune, in exchange for “a few of my rare lice.” She complies, telling him everything that will happen in the rest of the book: He’ll meet a donkey, ride him to a knight, fight and beat that knight, meet a hideous princess, and marry her. Today’s anti-spoiler culture warriors would throw a fit over that page of the book, which leaves virtually nothing else to discover in the story.

But as with Steig’s other writing, the point of Shrek! isn’t the action, it’s another early-readers’ philosophy treatise. Shrek is catastrophically ugly — again, he somehow has laser-eyes just because his face is so grotesque — but he’s happy exactly as he is. He’s happy in virtually every circumstance, in fact — that big enthusiastic grin on his face when his folks are full-on kicking him in the ass is entirely typical. When he meets a murderous dragon, he smiles because he knows it can’t hurt him, and he knocks it out by breathing flame in its face. When he enters the princess’ castle, he experiences fear for the first time because he winds up surrounded by “hundreds of hideous creatures.” Then he realizes what he’s looking at.

“He lashed out at the nearest one,” Steig writes, “but what he struck was glass. Shrek was in the Hall of Mirrors. ‘They’re all me!’ he yodeled. ‘ALL ME!’ He faced himself, full of rabid self-esteem, happier than ever to be exactly what he was.”

To some degree, Shrek! is just an absurdist story, written to be funny to little kids because it feels like a trip through Opposite Day. It’s funny for the same reason so many young kids find it hilarious to put their shoes on their hands, or their pants on their heads — it’s a harmless inversion of normalcy. Shrek! similarly flips the world so that being ugly is a net positive, scary things like dragons are just funny and harmless, and the monster is the hero instead of the villain. When Shrek enters the castle at the end of the story (carried there by a donkey, who only appears on three pages of the book, and has so little personality that it’s mildly hilarious how much he came to dominate the movies), he meets “the most stunningly ugly princess on the surface of the planet,” and they immediately start talking to each other in poetry:

Said Shrek: “Your horny warts, your rosy wens, like slimy bogs and fusty fens, thrill me.”

Said the princess: “Your lumpy nose, your pointy head, your wicked eyes, so livid red, just kill me.”

Said Shrek: “Oh ghastly you, with lips of blue, your ruddy eyes, with carmine sties, enchant me. I could go on, I know you know the reason why I love you so — you’re ugh-ly!”

Said the princess: “Your nose is so hairy, oh let us not tarry, your look is so scary, I think we should marry.”

And that’s the bigger philosophical lesson of Shrek!, the one that carried over to the movie even when virtually all the other details were dropped or changed: self-esteem and confidence matter more than looks. (And perhaps secondarily: There’s someone out there for everyone who eventually wants to end up in a relationship.) Stated in such a straightforward way, that sounds like a message suited for just about any kind of children’s book, from ultra-sincere teaching stories to this kind of utterly absurdist adventure. Shrek! is just the only book out there that aims to boost kids’ self-esteem and self-acceptance through a mottled green mutant-man with laser eyes, fire breath, and a carefully curated collection of lice.