a chicken-and-egg situation

a ˌchicken-and-ˈegg situation

a situation in which you do not know which of two connected events is the cause of the other: Is she unhappy because she gets into debt, or does she get into debt because she’s unhappy? I suppose it’s a chicken-and-egg situation.This comes from the question ‘Which came first — the chicken or the egg?’.
See also: situation