Every once in a while I pluck it out, marvel at its shininess, and then gently bounce it in my hand to feel its weight.

Someone left it where I was sure to find it. I don't know who - it's a mystery of life. I like mysteries of life.
But, it's not just any shiny blue sphere. It's a bearing ball.* I love bearing balls as much as I love marbles - well maybe a bit more.
*I usually call them ball-bearings, but Wikipedia corrected me.