Why is the narrator's brother nicknamed doodle?

The narrator's brother is nicknamed Doodle because he was physically frail and unable to walk as a baby, leading to his unusual crawling style that resembled the motion of a doodle or scribble. The name also reflects the narrator's initial disappointment and embarrassment about his brother’s limitations. Over time, however, Doodle's charm and resilience endear him to the narrator, and the nickname takes on a more affectionate tone.