On a basic level, it is the internal reflection of light, in a chamber with excited atoms, that gives a laser its coherence. The laser needs no focus to shine a straight beam, it just needs to be carefully released.
On a basic level, it is the internal reflection upon values, in a brain excited by thought, that gives a person a coherent purpose in life. Such a person needs no focus to walk a straight path, just careful expression.
Suffice it to say that lasers, light of one frequency travelling in phase, and an individual, with one primary goal directing her/his actions, have many memes in common.
A focussed coherence, under varying circumstances, might travel unimpeded, strongly illuminate without any obvious effect, or utterly overwhelm its target. Usually, the result can be predicted, based on the situation, but one never really knows all that might be important in achieving a result. Without a chain of events that gives focus, actions and emissions travel willy-nilly, with no unity of purpose, going everywhere and nowhere.
So here I write, recognizing that a certain chain of events have indeed given me a focus. I have started a journey toward a target, not knowing all that might be important along my way.
I must doubt, so that I never take for granted what I might or will achieve. I must doubt, or else all is for nothing.
Of course I doubt.