Some readers remember The Giving Tree as a sweet picture book about the strength of unconditional love. To others, it was a heartbreaking tale that messed them up during story time. No matter your interpretation of the story, The Giving Tree is a children’s classic that helped make Shel Silverstein a household name—even if it took him a while to get there.

1. Multiple publishers rejected The Giving Tree.

Shel Silverstein had only sold one children’s book—Lafcadio: The Lion Who Shot Back—when he went about finding a publisher for The Giving Tree. The book’s somber themes made it a hard sell. One editor at Simon & Schuster described it as “too sad” for kids and “too simple” for adults, while another editor called the titular tree “sick” and “neurotic.” Other publishers were moved by the story, which follows the relationship between a boy and a tree over the course of his lifetime, but ultimately felt it was too risky for the genre. After four years of searching for a publisher, Silverstein finally found a home for the book at Harper Children’s, when editor Ursula Nordstrom recognized its potential.

2. The Giving Tree was a surprise success.

The Giving Tree received a small release in 1964 with just 5000 to 7500 copies printed for the first edition. Though its publisher clearly underestimated its potential popularity, it didn’t take long for the book to explode into a modern classic. It quickly became one of the most successful children’s books of the era and made Silverstein an important figure in the industry. Today, nearly 55 years after it was first published, The Giving Tree has sold more than 10 million copies worldwide.

3. There are various interpretations of the relationship at the center of the story—not all of them positive.

The Giving Tree centers on the relationship between a tree and a boy throughout the stages of his life—from his childhood to his elderly years. In each stage, the tree provides the boy with whatever he needs, ultimately giving him a stump to sit on when the tree has nothing else to give. Positive interpretations of this story paint it as a parable of unconditional love: When it first hit shelves, The Giving Tree was a hit with Protestant ministers, who applied Christian themes to the book. But according to some critics, the book depicts an abusive relationship, with the tree literally allowing herself to be destroyed to keep the perpetually dissatisfied boy happy while receiving nothing in return. Other interpretations compare the relationship between the tree and the boy to those between a mother and child, two aging friends, and Mother Nature and humanity.

4. The author’s photo is infamous.

The author’s photograph on the back of The Giving Tree—depicting a bearded, bald-headed Silverstein glaring at the camera—has gained a reputation of its own. A Chicago Tribune writer called it “demonic” while a writer for NJ.com pointed out his “jagged menacing teeth.” In the children’s book Diary of a Wimpy Kid: The Last Straw, there’s an entire passage where the main character’s dad uses Silverstein's photo to terrorize his son into staying in bed.

5. The Giving Tree isn’t Shel Silverstein’s favorite work.

The Giving Tree may be among Silverstein's most successful and recognizable works, but when asked what his favorite pieces of his writing were in a 1975 Publisher’s Weekly interview, he left it off the list. “I like Uncle Shelby's ABZ, A Giraffe and a Half, and Lafcadio, The Lion Who Shot Back—I think I like that one the most," the author said. But that doesn’t mean he isn’t proud of the book that helped launch his career. On the book’s popularity, he said "What I do is good ... I wouldn't let it out if I didn't think it was."

6. Silverstein dedicated The Giving Tree to an ex-girlfriend.

The Giving Tree’s short dedication, “For Nicky,” is meant for an old girlfriend of the children’s book author.

7. Silverstein hated happy endings.

In case The Giving Tree doesn’t make it clear enough, Silverstein stated in an 1978 interview that he detests happy endings. He told The New York Times Book Review that he believed cheery conclusions “create an alienation” in young readers. He explained his stance further, saying "The child asks why I don't have this happiness thing you're telling me about, and comes to think when his joy stops that he has failed, that it won't come back." The Giving Tree features what is perhaps Silverstein’s best-known sad ending, if not one of the most infamous endings in children’s literature.