What makes a thing truly useful?

I was cleaning the seed trays this morning and noticed how the old wooden ones—chipped, uneven, stained with years of soil—still hold better than the new plastic ones. Not because they’re sturdier, but because they’ve earned their place. I keep wondering: is usefulness just habit? Or does it live in the weight of use, not the design? What’s something you rely on that no one else would call practical?