Relishing a rare opportunity to work from home for the afternoon, on a beautiful sunny winter day, I make my way to my flat in the Inner Sunset as usual, until, I was struck by the sudden sober notion that I may not have my house keys.

Frantically emptying my bag of all its contents, I don't see them. Wildly searching my memory of the last times I laid eyes on them, I search again -- cursing myself for needing to do so.

It can't be! -- but it is. Yes: I forgot my keys. Now, stranded on the sidewalk in front of my home, wistfully watching everyone else who has someplace to go, I wonder what to do next.

I can't believe that after all those times I'd been sure to pause on the way out the door in order to lay my hands on that key before exiting -- that precaution obviously slipped my mind today. Of all days.

Who would have thought that a tiny two-inch piece of metal could tip the scale of my entire day?