In Stave 2, we get some glimpses into Scrooge’s past that tell us why he acts the way he does. At school, he was left all alone on the holidays with no one there but books to keep him company.
When Scrooge is first taken back to his childhood school, he is thrilled to see his old classmates.
The jocund travellers came on; and as they came, Scrooge knew and named them every one. Why was he rejoiced beyond all bounds to see them! Why did his cold eye glisten, and his heart leap up as they went past! (Stave 2, p. 20)
Scrooge is thrilled! When the ghost takes him inside, he cries. He knows that what he will see will not be a pleasant memory. When his mother died, his father sent him away to boarding school and did not come to get him for holidays. Scrooge had to stay in the empty school all alone.
“It's dear old honest Ali Baba! Yes, yes, I know! One Christmas time, when yonder solitary child was left here all alone, he did come, for the first time, just like that. Poor boy! (Stave 2, p. 20)
When Scrooge was all alone, the books were his only comfort. The characters became his only friends. Scrooge remembers their adventures well, and recounts them “in a most extraordinary voice between laughing and crying” (p. 20). When he sees Robinson Crusoe, he asks where he has been.
Books cannot replace real people, and real friends. The spirit pities the lonely child. Scrooge remembers the boy singing at his door, and wishes he had been kinder to him.
The "solitary boy" is the young Ebenezer Scrooge, himself. His only friends for the holidays are the literary, imaginary characters from the books he is reading, such as Ali Baba ("1001 Arabian Nights") and Robinson Crusoe ("Robinson Crusoe").
Read Stave II of "A Christmas Carol" by Charles Dickens for the extended scene.