One of the most common motifs in Slaughterhouse-Five is the phrase “so it goes.” Billy Pilgrim learns the phrase from the Tralfamadorians and the narrator uses it whenever there is a mention of death. Each time a person dies or a tragic event results in death, the phrase "so it goes" is appended to the paragraph. The phrase may seem like a flippant, dismissive way to deal with death, but it reflects the different way in which the Tralfamadorians view the world. Death is not unexpected or tragic for the aliens, as they experience time in a different way. A person may die in a specific moment, but they continue to live in the past, at the various other times when they were still alive. All of these times happen at once, so death is just another moment in a universe of such moments. It is a natural byproduct of the passing of time, though it is by no means final. “So it goes” encapsulates this idea of death as another element of a complicated and infinite conception of time.

The phrase illustrates how violence and death can desensitize people to reality. The phrase is repeated so often in the book that it becomes a mantra.