As young Jody Tiflin grows up on his father's horse and cattle ranch, he learns that life is not for slacking. Every day there are chores to do, animals to care for, and all kinds of responsibilities to attend to. Though he is only a boy, his duties are many and, to his credit, he seldom complains. But sometimes, a person's duty can overwhelm him, as it does Billy Buck. In The Red Pony, the key is not to give up. You've got to keep on trucking, no matter how hard, painful, or rainy it gets.
All this talk of a person's duties is nonsense. The Tiflins have no other choice than to carry out their many responsibilities. If they didn't, the ranch would fall to shambles. It's not their duty to take care of things. It's just life.
Billy Buck is flawless in performing his many responsibilities. Just because he told Jody it wouldn't rain doesn't mean he shirked his duty to care for the animals. It was bad luck. That's all.