In The Things They Carried, the overall mood is stark and somber, but also intimate and contemplative. Throughout the collection, the mood undergoes frequent shifts. The reader gathers this already in the first and titular story. On one level, the mood in this story is shaped by Jimmy Cross's longing for Martha. On another level, it is shaped by the pragmatic yet overwhelming lists of equipment that the men carry with them through Vietnam. However, these lists feature a wide range of registers: they carry rations and weapons, but also comic books, pantyhose, diaries, diseases, and ghosts. The variation in the physical and intangible things the men carry gives an idea of the multifaceted mood in each individual story and the collection overall. In some of the more serious moments, the soldiers make jokes or say something that punctures the reigning gravity. There are many instances in which the mood is genuinely comical or sweet.
Again and again, O'Brien demonstrates his commitment to the idea that a story is never one single thing. By playing with language and chronology, he pairs darkness with lightness, gravity with levity, and pain with humor. In "Spin," he describes this approach through a simile: "On occasions the war was like a Ping-Pong ball. You could put fancy spin on it, you could make it dance." Although he never makes light of the war or shies away from how awful it was, he acknowledges that calling war hell does not capture "the half of it," because it is also "mystery and terror and adventure and courage and discovery and holiness and pity and despair and longing and love." He can offer the reader "bloody stories," but also "happy stories," and "even a few peace stories." By including stories of all of these natures—and more—side by side, O'Brien shakes up the mood and attempts to paint a more honest, wide-ranging picture of the war.