It doesn't happen with the suddenness of a flashlight but it does anyway - silently, surreptitiously and almost like a cat sneaking from behind and leaping at some crumbs on our trousers.
We feel that we got it all sorted out and dismiss the cat as inconsequential but the damage has been done, the crumbs are no longer there, and yet we move on without realising that something substantial is missing.
And then after many months or even years, we begin to recognise the changes, and begin noticing the subtle shifts in our physical and mental geography. We wonder if it's the same person we know or wonder if we've been transformed into something else: someone disagreeable, someone strange, someone unrecognizably alien.
And then it dawns upon us... it was that moment when it happened, that moment that didn't seem unusual at the time or even out of the ordinary, and yet... we realize that it was that moment that triggered everything.