Bilbo kept the Arkenstone because he is aware of the fact that it is very important to the dwarves, especially Thorin. Ever since the dwarves entered the Lonely Mountain they have developed a sense of greed. In fact, Thorin would do anything to get his hands on the stone. Bilbo knows that if the Arkenstone is in his possession he can use it as demand later on during the journey, especially in a tough situation. Bilbo justified his decision to withhold the discovery of the Arkenstone from Thorin by stating (to himself), “They did say I could pick and choose my own share; and I think I would choose this, if they took all the rest!” (Pg. 237). Bilbo should have the right to the stone because he is the only one in the expedition who deserves it.