It can be a shocking thing.
In that moment, one of two things happens: either one's worst fears are realized or (less frequently) one is surprised by a reaction that was unexpected.
Sadly, the former is usually the case, something that leaves one reeling the moment after it happens. The moment can never be called back of course, no matter how hard the other person tries or even pretends that it never happened in the beginning. The truth is there, stark and unyielding, in a moment that a novel cannot express and and a cinematic trilogy cannot gloss over.
That moment is the like the splitting of an atom, where the waves of power and destruction ripple around and through one while, somewhat shockingly, everything else in the room remains completely static. To the outside eye, nothing has changed in the least. The only evidence of devastation is in the eye's and the unseen realm of the soul, which suddenly resembles the burned-out court in a housing development overrun by fire.
We are a polite society of course, so we tidy ourselves up and pretend that somehow nothing significant has really happened. An apology may be offered and accepted - as much for appearances as anything else - and the day continues on as if nothing had really happened.
Excepting, of course, the pain in our heart and the dimming of our vision with what might be tears.