Chinese Proverbs 刀不磨要生锈，水不流要发臭

dāo bù mó yào shēng xiù, shuǐ bù liǔ yào fā chòu
刀 不 磨 要 生 锈， 水 不 流 要 发 臭

 A knife will rust if not sharpened regularly, and water will stagnate if it is not allowed to flow.

解释 ( paraphrase )
刀要经常磨，不磨就容易生锈；水要不断流，不流就容易发臭。
这条谚语告诉我们：人要不断学习，不断进取，否则就会落后，甚至变坏。身体也要经常活动锻炼，否则就会生病。

This proverb denotes that one has to keep studying to avoid falling behind or even degenerating, and to keep doing physical exercises to prevent sickness.

造句 ( example )
刀不磨要生锈，水不流要发臭，人不学要落后，现代社会就是一个学习型社会，没有谁能够不学习，还能在竞争中生存的。