What is a specific, good thesis/theme for "The Rocking-Horse Winner"?

The story has an easily identifiable theme: Greed destroys love, affection, and, in some cases, life.

The two modes of realism mixed with the supernatural in “The Rocking-Horse Winner,” is a fantastic story that takes great pains to create a generally realistic atmosphere and to have its characters respond to external stimuli in the ways that “normal” people would. To win the attention and love of his nother, Paul is able to pick winning horses through a frenzied and debilitating ride on a rockinghorse.

All the family members have secrets. The mother’s secret is that “at the center of her heart was a hard little place that could not feel love, no, not for anybody” (paragraph 1). Paul’s secret is that, by furiously riding his wooden rocking-horse, he is often able to predict which horses will win races. Bassett’s secret, and Uncle Oscar’s, is that they profit from Paul’s predictions, even while the boy is on his deathbed. Their winnings are kept secret. Paul gives his mother 5,000 pounds, but does it anonymously. The house itself whispers a secret, “There must be more money” (5, 6, 181). The three children hear the whisper, but no one talks about it.

Each family member is also motivated by greed. It is the desire for more money that motivates them all. Perhaps the most blatant evidence of the family’s obsession with riches appears in Uncle Oscar’s attempt to console his sister after her son’s death: “My God, Hester, you’re eighty-odd thousand to the good and a poor devil of a son to the bad” (244)—as if he were enumerating her assets and liabilities on an imaginary balance sheet. Paul’s frenzied pursuit of money differs from the greed of the others in that he wants wealth not for himself but for his mother. Clearly he hopes that, by being “luckier” than his father, he will win his mother’s love and attention.

Irony is also present in the story. Paul, intent upon stopping the whispers in the house, anonymously gives his mother 5,000 pounds as a birthday present. Ironically, his gift has the opposite effect. The whispers grow louder. Given his mother’s insatiable greed for money, this result comes as less of a surprise to the reader than to Paul. There is irony in the story’s title. Paul, the rocking-horse winner, loses his life. Ironic, too, are Paul’s final words: “I am lucky” (241). In his mother’s definition of luck, in paragraph 18 (“It’s what causes you to have money”), Paul is lucky, of course—or was.