What is wrong with Doddle in The Scarlet Ibis?

In "The Scarlet Ibis," Doddle is the nickname given to the narrator's younger brother who is born with physical disabilities and struggles to keep up with his older brother's expectations. The main issue with Doddle is that he is unable to fully participate in the physical activities and adventures that the narrator tries to engage him in, which ultimately leads to tragic consequences. Doddle symbolizes vulnerability and the impact of unrealistic expectations on those who are different.