moment of truth

the moment of truth (a crucial moment; a critical or decisive time, at which one is put to the ultimate test, or has to make an important decision or when you can see if something has been successful or not) — момент истины; решающий момент; самый ответственный момент

Example 1: The moment of truth came when I had to decide whether to move in with Jim or get a flat on my own. (CIDI)

Example 2: Now that all the bills are in, we've come to the moment of truth — can we afford to live here or not?

A literal translation of a Spanish expression (el momento de la verdad) for the moment in a bullfight when the matador kills the bull. It was first used in English in Ernest Hemingway's story Death in the Afternoon (1932).