What happens when Paul gives his mother her birthday present?

Paul's mother is a terribly greedy individual, and the birthday present is solid evidence supporting this characterization. Paul very selflessly and lovingly decides that he would like to give his mother $5,000 for her birthday; however, he wants to do it $1,000 at a time. That way, he can spread out the money over 5 birthdays. It's a great concept, and his mother should be ecstatic about that kind of gift. That is what Paul thinks too, and he is very excited to see his mother's reaction to the news of the money. Unfortunately, the mother is so materialistic and greed orientated that she is actually disappointed in the annual installment condition.

“Didn’t you have anything nice in the post for your birthday, mother?” said Paul.
“Quite moderately nice,” she said, her voice cold and hard and absent.
She went away to town without saying more.
But in the afternoon Uncle Oscar appeared. He said Paul’s mother had had a long interview with the lawyer, asking if the whole five thousand could not be advanced at once, as she was in debt.

She eventually gets her hands on the entire amount, and she begins living a life filled with more luxury items; however, she simply isn't content with what she has. She wants more and more, and the $5,000 simply isn't enough anymore.

“There must be more money! Oh-h-h; there must be more money. Oh, now, now-w! Now-w-w – there must be more money! – more than ever! More than ever!”

This unrestrained greed and materialism from Paul's mother eventually leads to the tragic death of Paul.

Paul wins £5,000 betting on the horses. He's determined to step into the role vacated by his father and provide for his family. More than anything else, he's motivated by a desire to break his mother's streak of bad luck, which includes taking a wholly unsuitable man for a husband. Once Paul's won all that money, he wants to give it to his mother as a gift, to convince her that she really isn't as unlucky as she thinks she is. He plans to give her the money in installments, instead of all at once. That way, she'll feel lucky more than once over time. Unfortunately, Paul's mother doesn't feel lucky at all on receiving the gift. Her obsession with money has made her greedy, and so her response to Paul's generous gift is to demand even more, which eventually leads to tragedy.