In "The Rocking-Horse Winner," what idea fills the people in Paul's house with anxiety?

In this short story, the mother, Hester's, perception that there's not enough money fills the house with anxiety. Paul, her sensitive young son, constantly feels the pressure of his cold-hearted mother's discontent. To him, the very walls of the house seem to be saying more, more, we need more money. That his mother's discontent is irrational becomes apparent when Paul, with the help of his Uncle Oscar and a servant, wins 5,000 pounds betting on horses. The money, a large amount in that time period, simply isn't enough for the insatiable Hester. Instead of finding contentment, she immediately spends the winnings and wants more. Paul, too young to recognize that no amount will ever satisfy his mother, works harder and harder to please her, riding his rocking horse with greater and greater fury so he can discern which horse will win the next race. In the end, Paul's response to the anxiety in the household costs him his life.