The word perfect comes from the Latin perficere, per (complete) and ficere (do). Something considered perfect is that which is completely done; it exists in a state of completion, wholeness, perfection. When we describe something as perfect, what we’re saying is that there’s nothing we could add to it to make it better. Nothing more is needed because you can’t add to something that’s already whole.
Think of someone you love. Now think of the sound of that person’s laughter. Is that sound not perfect? There’s nothing you could change about that laughter to make it better; it’s already complete, it’s already whole. We use the word perfect to emphasize completeness. When you say someone is a “perfect stranger,” you’re not saying they’re a flawless stranger, you’re saying they’re a complete stranger to you. You’re not flawless—none of us are—but you are whole, you are complete, and you are perfect.
Katherine Morgan Schafler, The Perfectionist’s Guide to Losing Control: A Path to Peace and Power, Penguin Books.