second nature
变得习以为常，变成一种本能或习惯的行为
日常·形容习惯成自然
英文释义
something that is instinctive or habitual to someone, acquired through frequent repetition or long practice
例句
Driving on the left side of the road is second nature to him now.
典故来源
源自亚里士多德哲学，指通过反复实践形成的本能行为。