How much of what goes on in our lives do we choose, and how much is chosen for us? This is another question that hangs in the background of "One of the Lives." The speaker seems to be suggesting that fate is more important than free will. All of these trivial things—what the speaker writes on his college exam, the job his father takes, the death of a soldier he doesn't even know—work together to bring our speaker to where he is now. Sick. On a cot. In a farmhouse. Good times. What's more, he didn't have any say in most of the things he reports to us—they just happened, they were fated to be. All these small details (and an infinite number of others not mentioned) came together to put the speaker where he is at this moment: staring out the window and listening to plums dropping from their branches. Talking about it all "falling" into place (sorry, we couldn't resist).
According to this poem, life is just a happy accident (high five!) brought about by a bunch of small and unrelated events.
According to this poem, life is a brought about by a series of choices people make (no pressure or anything). Fate doesn't have much to do with it at all.