***force of habit: a tendency always to do things in a certain way because you have always done them in that way 出于習慣,習慣使然
I don't know why I check all the locks every time I leave the house. It's force of habit, I suppose. 我不知道為什么每次出門都要把所有的門鎖檢查一遍,我想是出于習慣吧.
***force of circumstance: a situation in which you are forced to do sth by factors beyond your control 迫不得已,情勢所逼
He claimed he turned to crime through force of circumstance. He hadn't been able to find a job and his family was starving.他聲稱自己犯罪是迫不得已.他找不到工作,一家人都在挨餓.