The film's title is taken from a line of William Wordsworth's poem "Ode on Intimations of Immortality from Recollections of Early Childhood":
Bud's parents are disappointed by, and ashamed of, his older sister—she is sexually promiscuous, smokes, drinks, and has had an abortion—and accordingly 'pin all their hopes' on Bud.
As the story progresses, Deanie is driven close to madness and institutionalized. Bud's family loses its fortune in the Great Depression, which leads to the father's suicide; and Bud takes up farming, which he had postponed because of his father's aspirations for him.
In the final scene, Deanie, home from the sanitorium after two and a half years, goes to meet Bud. He is now married to the daughter of Italian immigrants; he and his wife, whom he met while complying with his father's desire that he attend Yale University, have an infant child. After their brief reunion, Deanie and Bud see that they must continue their lives separately.
In the first, Deanie's mother encourages her not to give up her virginity to Bud, telling her "Boys don't respect a girl they can go all the way with; boys want a nice girl for a wife". Having bid her daughter a good night, Mrs. Loomis then talks with her husband, enthusiastically informing him that their daughter and the son of the richest family in town are in love and that Bud would "be the catch of a lifetime".
In the next scene, Bud's father encourages him to abstain from sex with Deanie, because, if the two of them were to conceive a child, they would have to marry.
Deanie's mother believes that sex would ruin her daughter's chances of marrying Bud. Bud's father believes that sex, especially pregnancy, would force his son to marry Deanie. One parent wishes for such a marriage, while the other seems to warn against it.
In their discussion of what kind of girl a boy wants as a wife, Mrs. Loomis also tells Deanie that "No nice girl" has sexual desires for a boy. When Deanie asks her mother whether she was ever sexually attracted to Mr. Loomis, the answer is "Your father never laid a hand on me until we were married. And, then, I—I just gave in because a wife has to. A woman doesn't enjoy those things the way a man does. She just lets her husband come near her in order to have children." This enhances Deanie's inner struggle—about whether to give Bud what she and he both seem to want, or whether to behave in a more socially acceptable way, avoid the risk of pregnancy, and follow her mother's advice about how to retain Bud's respect, which eventually drives her to madness.
Warren Beatty and Natalie Wood were to be paired also for the film adaptation of West Side Story, which was released eight days after Splendor. (Contenders other than Beatty for West Side's Tony role included Elvis Presley, Bobby Darin, and Anthony Perkins; but Richard Beymer won the part.)
The movie ranked number 50 on Entertainment Weekly's list of the 50 Best High School Movies