A well-used door needs no oil on its hinges. A swift-flowing steam does no grow stagnant. Neither sound nor thoughts can travel through a vacuum. Software rots if not used.

• 经常使用的门不需要往门轴里上油。流动的东西就不会停滞不前。声音和思想都不能在真空里传播。软件不用就会腐朽。