The opening tone of Claudia's remark is one that equates how the condition of the world is the result of human action. Claudia accesses a theory of correspondence: The natural world is a reflection of human action. As old as Shakespeare, this idea shows how the natural world mirrors the human condition. Humans do bad things, the natural world reflects it. Pecola's father rapes and impregnates her, the marigolds do not grow. There is a note of optimism in this construction. Human misdeeds is reflected in nature, therefore if human actions are good, nature can reflect this. It is optimistic in that the cause and effect relationship shows the power of the individual. The cause and effect sequence that is offered is one in which the natural world mirrors individual action.
Yet, Morrison is able to invert this as the narrative continues. Claudia's reflection suggests that there is not a one to one ratio between human interaction and the natural world. She challenges the theory of correspondence, suggesting that the natural world itself might be corrupted, of which human action merely reflects a condition of victimization and eternal suffering:
For years I thought my sister was right: it was my fault. I had planted them too far down in the earth. It never occurred to either of us that the earth itself might have been unyielding. We had dropped our seed in our own little plot of black dirt just as Pecola's father had dropped his seeds in his own plot of black dirt.
Initially, Claudia believes that the marigolds don't grow because of the horrific actions of Pecola's father. The human initiation theory of cause and effect is evident. Yet, upon reflection, it becomes clear to her that the natural world itself is impure for it allows and almost permits the victimization of the individual. Pecola is the universal victim that suffers abuse from everyone. She is never given a sense of love and sanctuary that will allow her, as a marigold of and in this world, to grow. Claudia's reflection is what enables her to assert that "the earth itself might have been unyielding." In this light, there is no real sense of distinct cause and effect. There is only the effect of suffering, something that becomes a permanent part of Pecola's being in the world.