How does the symbolism of the ibis support the theme of "selfish pride generally causes more harm than good"?

Brother’s selfish pride allowed him to teach Doodle to walk, but he pushed him to hard and he died because of it. 

Brother considers the ibis symbolic of his brother’s condition.  The ibis lands in their yard, and it is too delicate to survive.  Doodle is attracted to it, and feels an affinity for it.  He too is delicate and unable to survive. 

Through hard work and a desperate determination, Brother is able to...

Brother’s selfish pride allowed him to teach Doodle to walk, but he pushed him to hard and he died because of it. 

Brother considers the ibis symbolic of his brother’s condition.  The ibis lands in their yard, and it is too delicate to survive.  Doodle is attracted to it, and feels an affinity for it.  He too is delicate and unable to survive. 

Through hard work and a desperate determination, Brother is able to teach Doodle to walk for his sixth birthday.  It is an act born of pride.  He wants a brother like everyone else’s. 

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. 

Brother pushes Doodle, and when he cries he asks him if wants to learn to walk.  Doodle desperately wants to please his brother.  His brother is pleased when Doodle learns, and so is the entire family.  It isn’t enough, though, for Brother.  He wants to make his ibis stronger than he is.

Having taught his brother to walk, Brother pushes harder.  He wants Doodle to be normal.  He wants him to be able to run and play.  He pushes too far this time, and Doodle collapses. 

I began to weep, and the tear-blurred vision in red before me looked very familiar. "Doodle!" I screamed above the pounding storm and threw my body to the earth above his. For a long time, it seemed forever, I lay there crying, sheltering my fallen scarlet ibis from the heresy of rain. 

It was Brother’s pride and arrogance that led to Doodle's death.  He refused to give up.  He pushed beyond the point of rational help, because he was thinking of what he needed, and not what Doodle needed.  He did more harm than good.