a situation in which it is difficult to tell which one of two things was the cause of the other
A CHICKEN-AND-EGG SITUATION, PROBLEM, ETC.
Meaning of A CHICKEN-AND-EGG SITUATION, PROBLEM, ETC. in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005