How does Elya get cursed in Holes?

In "Holes" by Louis Sachar, Elya Yelnats gets cursed after he fails to fulfill a promise to Madame Zeroni, a witch who helps him with his love for a girl named Myra. After carrying her up a mountain to drink from a spring as part of the deal, Elya becomes distracted by Myra's beauty and does not return to carry Madame Zeroni up the mountain in return. As a result, she curses him and his descendants, leading to a life of misfortune for Elya's family. This curse is a central theme that affects the generations of the Yelnats family throughout the story.