Earlier today I was driving a car that belongs to someone near and dear to me. It looks good, is comfortable to drive, and seems to be in good working order. Up ahead there were some cows walking along side the road. I put my hand over the center of the steering wheel in case I needed to lay on the horn to keep them from jumping out in front of the car. They paid no attention as I passed by, so just for fun, I honked the horn. Except the horn didn't honk. I pushed down a few more times, and tried different spots to see if I could get a beep. Nothing but the sound of silence.
My guess is that the owners don't even know it isn't working. A car horn is only there in case we need it. But if we haven't needed it for a while, we'll probably assume it is in good working order. We've got things to do, people to see, and nary a cow in sight. We won't notice that it isn't working until it's too late.
We all have our blind spots and can't always see when danger is headed our way. That's why we need each other.
As the saying goes, if you see something, say something.