一朝被蛇咬，十年怕草繩

Once bitten, twice shy.

一言既出，駟馬難追
A word spoken is past recalling.

一見鐘情
to fall in love at first sight

一箭雙鵰/一舉兩得
Kill two birds with one stone.

一寸光陰一寸金
Time is money.

一失足成千古恨
The error committed on impulse may turn out to be the sorrow of a whole life.

一將功名萬骨枯
What millions died that Caesar might be great.

一年之計(jì)在于春，一日之計(jì)在于晨
Plan your year in spring and your day at dawn.

一人難稱百人意
You cannot please everyone.

一氣呵成
Never make two bites of a cherry.?

小Car筆記：
on impulse：一時(shí)沖動(dòng)，一時(shí)心血來潮
turn out：結(jié)果是， 證明是