Why was Long John Silver excited when he thought that Captain Smollett was going to show him the chart of the island?

When the Hispaniola reached Treasure Island, Long John Silver appeared to believe that Captain Smollett was about to show him the actual map of the island, the one that Jim had found in Billy Bone's personal effects. Silver became quite excited at the prospect, but then he appeared to be equally as disappointed when he realized that the chart he was being shown was a reproduction of the map, not the map itself.
The reason that this turn of events seemed to disappoint Silver so much was because the actual map contained the instructions, written by the late Captain Flint, for finding the buried treasure on the island. Had Silver been able to see the map and memorize the instructions for finding the treasure, he and the pirates would have been able to set off after the treasure immediately upon landing on the island. They would not have needed to depend on the Englishmen leading them to the treasure, which was Silver's original plan, nor would they have needed to fight the Englishmen, which was the strategy once Silver realized that the pirates would not be patient enough to carry out his original plan.