A few weeks ago, I experienced a perfect day.
It wasn't perfect as it was happening. It was just a day. Some good stuff happened, some less-good stuff happened. I experienced moments of pleasure and moments of worry. Like I said, just a day.
It wasn't until evening that its perfection revealed itself to me. A question arose in my mind: "Of the things actually under my control, what of this day would I have changed?" The answer hit me with pugilistic force: of that under my control, I would have changed nothing.