Uncertainty and doubt vs. clinical inevitability. Tom is wary of people asking questions, Pa is wary of the buyers, Ma is weary of what happened to Tom in prison, Muley uncertain of his fate, and the preacher about his faith.
Meanwhile the tractors cut the land into even, perfect strips and the banks exact to every %. Yet even they are unsure how the system they work for works.
Man is a collection of doubts.