"The Rocking-Horse Winner" by D.H. Lawrence is a story of discontent in its worst form, and the one who suffers this affliction is Hester, Paul's mother.
From the opening paragraph her discontent is evident:
There was a woman who was beautiful, who started with all the advantages, yet she had no luck. She married for love, and the love turned to dust. She had bonny children, yet she felt they had been thrust upon her, and she could not love them. They looked at her coldly, as if they were finding fault with her. And hurriedly she felt she must cover up some fault in herself. Yet what it was that she must cover up she never knew. Nevertheless, when her children were present, she always felt the centre of her heart go hard. This troubled her, and in her manner she was all the more gentle and anxious for her children, as if she loved them very much. Only she herself knew that at the centre of her heart was a hard little place that could not feel love, no, not for anybody. Everybody else said of her: "She is such a good mother. She adores her children." Only she herself, and her children themselves, knew it was not so. They read it in each other's eyes.
Hester blames her discontent and her inability to love her children on having no luck and "some fault in herself"; however, she has plenty of luck but does not seem to realize it.
She "started with all the advantages" and has beautiful children, yet she is unable to find any love for them in her hard heart; in fact, they seem like an unwanted burden to them. The truth is that "at the centre of her heart was a hard little place that could not feel love, no, not for anybody." She is unable to love herself, and it is clear she fills that void by spending money.
Paul provides her with unexpected money, but she is not thankful; instead she spends it and is still predictably miserable. Her heart cannot feel love even when Paul dies trying to make her happy. As her son is breathing his last, "[h]is mother sat, feeling her heart had gone, turned actually into a stone."
The truth is that we do not know what, exactly, causes Hester's heart to be so hard. She married her husband for love, but that love "turned to dust." Perhaps that is what causes the hardness, but Lawrence is not clear about that. We know the hardness keeps her from loving her children, others, and even herself. She tries to feel something by spending money and buying things, but it is never enough. She "tried this thing and the other, but could not find anything successful." There is no relief or redemption in the story, as her hard heart actually turns into a stone at the end of the story.