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Bilbo initially has no intention or desire to leave with Thorin and the dwarves. The day before he'd been visited by Gandalf and had shown no interest whatsoever in accompanying him on any kind of adventure; "We are plain quiet folk and have no use for adventures. Nasty disturbing uncomfortable things! Make you late for dinner! I can't think what anybody sees in them."
The visitors (Thorin and 12 dwarves) believe Bilbo to be a burglar (exactly what Gandalf had in mind, and thus, the note), but Bilbo doesn't understand. He doesn't want to see a dragon or garner treasure, but his "Tookish" side is aroused (he inherited this from his mother). Golin then wisely points out that Bilbo is probably right and not up to the task. Yes, he was wise because the statement prodded at Bilbo's pride and made him determined to prove him wrong. Bilbo joined the dwarves the next morning without hesitation!
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