After Doodle shows his family that Brother has successfully taught him how to walk, Brother, in his role as narrator, offers some commentary to readers, using a metaphor in the process:
It seemed so hopeless from the beginning that it's a miracle I didn't give up. 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.
The metaphor here—in which Brother describes pride as “a seed that bears two vines, life and death”—foreshadows the fact that Brother’s desperation for his disabled brother to be seen as “normal” will lead to both positive and negative outcomes. Specifically, it leads to Doodle being able to experience more of “life” (as seen in his newfound ability to move through the world of his own accord), and, later, leads directly to his death. It is only because Brother becomes fed up with Doodle after a “failed” rowing lesson that he abandons Doodle during a storm, leaving him to die.
In this passage, Brother—who narrates this story from the future—demonstrates an awareness that his sense of self had become too tied to his brother’s “development,” and this prideful over-investment (and accompanying resentment) is what led to Doodle’s death.