The acting is great, including that of the supporting cast. Exaggerated at times, but after all, it’s satire. The witty screenplay by Billy Wilder and I. A. L. Diamond interweaves happiness, sadness, and the brief moments & little things that say a lot about our lives. For example, Miss Kubelik’s reference at a Chinese restaurant to “the same sauce, sweet and sour” is her way of commenting on the “sweet and sour” relationship she’s been in, and the broken mirror in her compact reflects how she feels. Recurring elements such as a record album by the piano player at the restaurant serve as signposts for viewers and links among the characters.
Some motifs occur many times, like the keys to the apartment and the executive washroom, which move among the employees of Consolidated Life. Others show up just twice, such as a tennis racket used as a spaghetti strainer, or the idea of sending someone a fruitcake every Christmas. Some references mark the times, such as TV ads for cigarettes, The Untouchables on Thursday evening, and the original Broadway production of The Music Man.
Wilder said this film was inspired by a scene in the English movie Brief Encounter (1946), in which a man takes the woman he’s seeing to the apartment of a friend. The friend returns early, and the woman goes out the back way. The return of the key in that film evolved into all the business about keys in The Apartment.