流水不腐， 户枢不蠹liú shuǐ bù fǔ , hù shū bù dù

running water is never stale and a door-hinge is never wormeaten; a man on the go (/progressing) corrupts(/stagnates) not; a thing in use (/on the move)rots not: constant practice keeps one’s hand in; drawn wells are seldom dry; practice keeps one from getting rusty; the oft-used key is always bright/“～”，是说它们在不停的运动中抵抗了微生物或其他生物的侵蚀。(《毛泽东选集》1045) The proverb“Running water is never stale and a door-hinge is never worm-eaten”means that constant motion prevents the inroads of germs and other organisms.