used at the end of a sentence to talk about why sth was done or whether it should have been done or not :
I still don't understand why you chose that name in the first place.
I should never have taken that job in the first place.
used at the end of a sentence to talk about why sth was done or whether it should have been done or not :
I still don't understand why you chose that name in the first place.
I should never have taken that job in the first place.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005