Peter loved to shop used articles. Almost a month ago, he bought popular word game that used little pieces of wood with different letters on them. As he was purchasing it, the salesgirl said, "Uh, look, the game box haven't even been opened yet. That might be worth some money. " Peter examined the box, and, sure enough, it was completely covered in factory-sealed plastic. And he saw a date of 1973 on the back of the box. "You should put that up for auction   on the Internet, and see what happens."the salesgirl said. "Yes, you're right. People like something rare." Peter agreed, "I can't imagine there being very many unopened boxes of this game still around 40 years later." "Don't forget to tell me if you sell it." the salesgirl smiled. "No problem." Peter said. After he got home, Peter went online to several auction websites looking for his game. But he couldn't find it. Then he typed in the name of the word game and hit Search. The search result was 543 websites containing information about the changes of the game. Over the years, the game had been produced using letters in different sizes and game boards in different colors. He also found some lists of game fans looking for various versions of the game. Peter emailed some of them, telling them what he had. Two weeks later, Peter went back to the shop. "Hello. Do you still remember the unopened word game?" The salesgirl looked at him for a second, then recognized him and said, "Oh, hi!" "I've got something for you," Peter said. "I sold the game and made $1,000. Thank you for your suggestion." He handed her three $ 100 bills. "Wow!" the salesgirl cried out. "Thank you, I never expected it." What is the main theme of the story?
It's important to keep a promise. It's great to share in other people's happiness. We should be grateful for the help from others. Something rare is worth a large amount of money.