steam sand for food—make fruitless efforts; waste one’s energy ? 算了吧！ 你只不過(guò)是在～而已！ Enough of that! You’re only making fruitless efforts like steaming sand for food.
蒸沙作飯zhēnɡ shā zuò fàn
把沙子蒸成飯。比喻根本不可能實(shí)現(xiàn)的事情。a hopeless task, waste one’s energy