What do I think?
I think, its simply about the 'two', it is this form of two possibilities, in difference to a form of three or four or more. It is this form of an opposition or double like "head or tail" that produces your narration about echoes of 'action and reaction' within ' expectation and event', 'hope and disappointment', 'fear and release'.
Your mind wants to force a handy 'cause and effect' to get a grip on an event simply by your expectation although the event is absolutely independent from your expectation. It is a psychological result of the 'hope for the best and expect the worst'.