What is brother's struggle with pride and in what ways or how in "The Scarlet Ibis"?
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The over-riding struggle that the author seems to have with pride has to do with how a little brother is a reflection of an older brother.
There are some age-old expectations we typically have of older brothers. We believe they will help younger brothers turn into men. We believe they will be protectors. We believe they will be teachers.
For Doodle's older brother, part of his problem is an unable playmate. Thus, Hurst is developing this theme of pride through characterization. We see how he depicts the older brother through narration with the truth that
"There is inside me (and with sadness I have seen it in others) a knot of cruelty borne by the stream of love."
He is pointing out that even in our good relationships, we can be mean.
His selfishness comes out most when the rains come in the end. He thought he had taught Doodle well enough that Doodle would run from the rain. But his death makes it appear that the rain was too much stress for his heart. The brother's departure from Doodle's voice and then apparent waiting for him left a mark of guilt on the brother forever. He doesn't even merit himself worthy enough of a name in the re-telling of this tale.
One of the best quotes that demonstrates this entire phenomenon is the brother's realization that,
"[He] did not know then that pride is a wonderful, terrible thing, a seed that bears two vines, life and death."
For Doodle and his brother, one vine was the work they accomplished, the other was the brother's avoidance of Doodle's shortcomings.