In "The Scarlet Ibis," the brother/narrator learns that his blind determination cannot alter Nature. For, in the exposition of the story, the brother remarks with hindsight,
But all of us must have something or someone to be proud of, and Doodle had become mine. I did not know then that pride is a wonderful, terrible thing, a seed that bears two vines, life and death.
When the brother finds himself embarrassed by Doodle, who cannot do things that are normal for children his age such as walking, he insists upon teaching Doodle to walk. Emboldered by his success, the brother narrates that he "began to believe in [his] own infallibility"; so, he pushes Doodle to accomplish other skills common to boys, such as swimming. And, although Doodle falls "behind schedule," the brother's "pride wouldn't let [him] accept defeat."
It is at this point in the story that Doodle significantly spots a scarlet ibis one day. Significantly, it is perched in a "bleeding tree," and is out of its environment of Florida or South America:
...amid much flapping and a spray of flying feathers, it tumbled down, bumping through the limbs of the bleeding tree and landing at our feet with a thud.
Angered that Doodle will not swim one day, the brother makes Doodle row against tide as they flee from an approaching storm. After they reach the shore, Doodle is exhausted. But, he tries to stay with his brother who walks quickly. As the brother runs with that "streak of cruelty" in him which faults Doodle for his failure to measure up, just as the scarlet ibis who also was caught in a storm and attempts to survive in an environment too hostile for its nature, little Doodle, too, succumbs and dies when he attempts to run in the storm. When the brother doubles back for Doodle, he finds him bleeding from his throat and lying awkwardly on the ground, just as the ibis has done, and "the tear-blurred vision in red...looked very familiar."