Nothing in the world is difficult for one who sets his mind to it.
世上无难事，只怕有心人。

Nothing is difficult to the man who will try.
世上无难事，只要肯登攀。

Nothing seek, nothing find.
没有追求就没有收获。

Nothing is so necessary for travelers as languages.
外出旅行，语言最要紧。

Nothing is to be got without pains but poverty.
世上唯有贫穷可以不劳而获。

Not to advance is to go back.
不进则退。

Not to know what happened before one was born is
always to be a child.
不懂世故，幼稚可笑。

No way is impossible to courage.
勇者无惧。
Obedience is the first duty of a soldier.
军人以服从命令为天职。

Observation is the best teacher.
观察是最好的老师。

Offense is the best defense.
进攻是最好的防御。

Old friends and old wines are best.
陈酒味醇，老友情深。

Old sin makes new shame.
一失足成千古恨。

Once a man and twice a child.
一次老，两次小。

Once a thief, always a thief.
偷盗一次，做贼一世。

Once bitten, twice shy.
一朝被蛇咬，十年怕井绳。

One boy is a boy, two boys half a boy, three boys no boy.
一个和尚挑水喝，两个和尚抬水喝，三个和尚没水喝。

One cannot put back the clock.
时钟不能倒转。

One eyewitness is better than ten hearsays.
百闻不如一见。

One false move may lose the game.
一著不慎，满盘皆输。

One good turn deserves another.
行善积德。

One hour today is worth two tomorrow.
争分夺秒效率高。
One man’s fault is other man’s lesson.
前车之鉴。

One never loses anything by politeness.
讲礼貌不吃亏。

One swallow does not make a summer.
一燕不成夏。

One’s words reflect one’s thinking.
言为心声。

Out of debt, out of danger.
无债一身轻。

Out of office, out of danger.
无官一身轻。

Out of sight, out of mind.
眼不见，心为静。
Patience is the best remedy.
忍耐是良药。

Penny wise, pound foolish.
贪小便宜吃大亏。

Plain dealing is praised more than practiced.
正大光明者，说到的多，做到的少。

Please the eye and plague the heart.
贪图一时快活，必然留下隐祸。

Pleasure comes through toil.
苦尽甘来。

Pour water into a sieve.
竹篮子打水一场空。

Practice makes perfect.
熟能生巧。

Praise is not pudding.
恭维话不能当饭吃。