The cost of a piece of metal in your eye.

I never wear my glasses (regular eyeglasses) when mowing, but one time for some reason I did, and that one time, a rock flew up and nailed me right in the middle of one of the lenses. Crazy good luck.

But I always always wear eye protection when doing anything in the garage. I wear them so religiously that sometimes I come inside and am wearing them around and my wife has to remind me to take them off, I don't even notice they're still on.