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.

一着不慎，满盘皆输。