The quote from "The Scarlet Ibis" speaks powerfully about the dangers of doing the right thing but for the wrong reason. In a society that might suggest that the end justifies the means, Brother's motivation to teach Doodle to walk is so that Brother doesn't have to be embarrassed by Doodle's weak body--not so that Doodle can have a better life. Doodle definitely wants to please Brother, but the physical tasks that he undertakes eventually kill him. When Doodle walks for his family, they are overwhelmed by the "wonderful thing" that has occurred, not realizing at that moment that it will lead to a "terrible thing."
When Doodle dies, Brother realizes that the end didn't justify the means at all. Brother's pride in improving Doodle is short-lived. In biblical terms, Brother learns the important lesson that "pride goes before destruction, a haughty spirit before a fall." Even worse, Brother's haughty spirit and pride do not merely cause him to fall; they cause the fall of Doodle. The few moments of a fully-achieved life that Doodle experiences hasten his death. Just like a vine can grow and twine around another plant, choking out the life force, so, too, does Brother's pride choke the life out of Doodle.
In the story, Brother had forced Doodle to learn many things that no one thought he could do. However, Brother's motivation for helping Doodle was pride, because he did not want anyone to think of him as a person with a handicapped brother. At first, everyone is amazed at the things that Doodle can do. These extraordinary feats are metaphorically the first vine pride can bring. However, once Doodle became old enough to go to school, Brother forced him to learn how to run because Brother didn't want to be embarrassed at school by Doodle's weaknesses. However, in pushing Doodle to run, Brother pushes too hard and Doodle dies. This is the second vine that pride can bring, death. Doodle gains more of life because of Brother's pride but in the end Brother's pride destroys Doodle because he is forced to do something he simply cannot physically accomplish.