What does Scout learn about Arthur Boo Radley at the end of the novel?

At the end of the novel, after walking Arthur "Boo" Radley home, Scout looks out at the view of town from the Radley's front porch. She notices just how much Boo could see just by looking out the window, since, being a recluse, was his only means of experiencing the world. She also notices just how clear the view of her house was, as well as the tree. Recalling all the times she, Jem, and Dill spent playing in plain view of the house, she realizes that in a sense, they were "Boo's kids", and he was actively a part of their lives, if only from the outside looking in.