By arc or by whole, the rainbow reveals refracted truth. Nearby rain and distant mist have equal power to vaporize visible light into bands of color. A single sheet of water, slicing through sunlight, projects the full spectrum against the sky's inverted bowl. If you are lucky enough to be standing far enough from the point where solar brilliance meets suspended water, you will see sunlight scattered into a full ring of color.
Like metaphorical truth, visible light rarely reveals its constituent parts so regularly and so predictably. Depart ever so modestly from the axis on which truth or light turns, and your eyes will no longer honor one focus. And if you should look instead at an object propelled through the sky, gravity's rainbow will no longer appear to you in closed form. It will rise — and fall — according to a trajectory that will never connect the beginning of truth with its end.
And this is to say nothing of the most treacherous trick of the light, the double deception that awaits time's pilgrim. Race toward the past if you will; yesterday recedes faster than your memory can recall. As you reel backward, redshift stretches memory beyond your field of perception, till truth dissolves in waves filled with heat rather than light. Race instead toward the future, and impatient anticipation crashes against the invariant pace at which tomorrow arrives. Against that blackness you will see no more than purple tendrils not quite taking full form, the fleeting projections of things yet to materialize.
Pivotal events therefore mark the sections of our lives, slicing at particular points of time through the whole of the truth and leaving us no more enlightened than the objects we trace across our field of vision at speeds well below that of light. Catch them, and you will be rewarded momentarily by the mirage of control. Miss them altogether, and you will rue forever the path that both of you, protagonist and projectile, must follow.