A theme is a message one tries to portray with a book. In Treasure Island, I would say that the theme is not relying on random people. The reason I say this is because Long John Silver, while appearing loyal and trustworthy on the outside, really causes the many hardships Jim and his group face. He hires the pirates and joins them in causing a mutiny, so they reach the island, Jim’s folks are left on land and the pirates take control of the ship. When the pirates go against Long John, he re-joins Jim’s group, and between the few men left alive after the story, they barely manage to make it from Treasure Island to South America, where they hire a new crew and go home to England. Long John Silver abandons them in South America, which is for the better, but the point is that he cannot be relied on. Therefore, I would say the theme of Treasure Island is not to rely on everyone you meet.