In J.R.R. Tolkien's fantasy novel The Hobbit, the dwarves gather at Bilbo Baggins' house because Gandalf told them that there was an expert "burglar" in the area "looking for a Job at once, and that he had arranged for a meeting here this Wednesday tea-time" (18). Gandalf, of course, intended for Mr. Baggins to be the fourteenth member of Thorin's company on a hunch that Bilbo might prove himself an invaluable asset to the dwarves' expedition to the Lonely Mountain; in fact, the old wizard becomes quite frustrated when the dwarves question his wisdom in choosing Bilbo and defends his selection by asserting "there is a lot more in him than you guess, and a deal more than he has any idea of himself" (Tolkien 19).
Bilbo had no idea of Gandalf's plans or intentions, so naturally the sudden appearance of thirteen dwarves on his doorstep at tea time befuddled the hobbit, especially when he believed to have only invited the wizard.
Gandalf made a sign on Bilbo's door signifying that this was where their burglar lives and where the dwarves should all meet up. Bilbo had no idea that the dwarves were going to show up and this caused him to panic. Gandalf appointed him as the person to be their burglar because he believed Bilbo would be the right person to bring them back to their home.