Many of today ’ s superstitions (迷信) are based on old beliefs (信念) . K nocking on the wood for good luck comes from the old idea that spirits (精灵) lived in trees. B reaking a mirror is bad luck because people once thought that reflections were part of a person ’ s spirit. P ulling apart the wishbone (许愿骨) of a chicken for good luck comes from old times when chicken bones were believed to have magical powers.