Why Don't They Teach Logic at These Schools?

The force of this quote-comparison will be much stronger for those who have read in full the stories from which both are taken (The Lion The Witch and The Wardrobe and The Princess and the Goblin.) Suffice it to say here that just as Lucy's siblings fail to credit her "imaginary country" and her friendship with a faun, so Curdie dismisses Irene's tale about her great-great grandmother and the existence of a certain magic thread. Their slowness to accept the truth is then gently rebuked by two grown-ups (Professor Kirke and Curdie's mother) who DO believe the young heroines-and whose past histories, once we know them, make this belief almost inevitable:

Logic!” said the Professor half to himself. “Why don’t they teach logic at these schools? There are only three possibilities. Either your sister is telling lies, or she is mad, or she is telling the truth. You know she doesn’t tell lies and it is obvious that she is not mad. For the moment then and unless any further evidence turns up, we must assume that she is telling the truth.”

— The Lion, The Witch and The Wardrobe, Chapter V, Back on This Side of the Door
...You have no right to say what she told you was not true. She did take you out [of the mountain] and she must have had something to guide her: why not a thread as well as a rope, or anything else? There is something you cannot explain, and her explanation may be the right one.
— The Princess and the Goblin, Chapter XXIII, Curdie and his Mother