a doorhinge never becomes wormeaten—constant activity staves off decay
戶樞不蠹
A door-hinge is never worm-eaten. —Constant activity staves off decay. 流水不腐，～(《呂氏春飲·盡數(shù)》) running water is never stale and a door-hinge never wormeaten(The Spring and Autumn Annales of Mr.Lv)