Short selling means that investors trade by borrowing or selling contracts without actually owning goods, hoping to make profits when commodity prices fall in the future. However, in order to protect market stability and prevent manipulation, the exchange will restrict or prohibit investors from short selling. When the number of futures contracts is insufficient, it means that the number of contracts available for trading in the market is limited, which is not enough to meet the needs of all investors. In this case, the exchange will temporarily ban short selling operations to avoid market instability and potential manipulation risks.