I Had No Idea
I power-washed this wall years ago. Over time, it slowly gathered more and more grime, and I didn’t notice how bad it was until I hit it with the sprayer by accident while doing the stairs nearby. When I saw the bright, warm concrete surface beneath the soot and filth, I knew what I had to do. Needless to say I took care of it, and afterward it looked like a brand new wall.
There’s probably a metaphor in here about regular doses of effort keeping the proverbial grime at bay so it doesn’t build up without us noticing.