One truth is clear, whatever is, is right. (Alexander Pope)
Goodness and being are really the same. Everything is perfect so far as it is actual. Therefore it is clear that a thing is perfect so far as it exists. (St. Thomas Aquinas)
The word "perfect" takes its origin from the Old French parfit, which in its turn stems from the Latin perfectus, which means "completed" (Online Etymology Dictionary).
If you consult a Latin-English dictionary for the word perfectus you will get "complete, finished, done/perfect, without flaw" (note the order of these meanings). JM Latin-English dictionary translates the verb perficio as "to complete, finish, execute, bring about, accomplish, do thoroughly" (once again note the order of meanings!).
Thinking of the word "perfect" in the connotation of "completed" rather than "complete" makes good sense. What's completed is complete. What has occurred, what has taken place, is already a fact. It can't be made into anything more than it is. One cannot add to a fact. A fact--just like perfection--is beyond improvement.
Put differently: completed = complete = perfect.
Or, as St. Thomas Aquinas implied, actual = perfect.
Or, as Alexander Pope similarly suggested, whatever is = perfect.
Or, as I put it, present (by virtue of being already a completed fact of life and, thus, beyond improvement) is perfect.
I know, it sounds like a 180-degree conceptual u-turn. It is. It is about time that we - as a culture, as a civilization - stop this tail-chasing pursuit of theoretical perfection and, for a change, acknowledge the ordinary perfection of what exists. It's about time we get out of this existential dead-end of trying to lasso an imaginary unicorn of the unattainable.