In Slaughterhouse-Five, Billy Pilgrim is always shown exhibiting passivity, a lack of caring about what is going on. For example, although he has the Serenity Prayer framed on his wall, he believed "the things [he] could not change were the past, the present, and the future." Thus, Pilgrim believes himself a passive observer of his life, incapable of changing a single thing. For example, he does not care in World War II when is is abducted by the Germans, and neither does he care about the excessive bombing in the following Vietnam War. His summation of the death of his dog, a normally tragic event, was "So it goes. Billy had liked Spot a lot, and Spot had liked him."

Vonnegut uses Billy's passivity to contrast his anti-war views. He uses Pilgrim to make a cold comparison to those who claim war is an inevitability. He shows Pilgrim as believing all things as an inevitability, and thus he simply idly stands by and lets tragedy take her course. So it goes.