Casting

I’ve never understood casting. I was watching a commercial this morning, and the father in the scene had to skip a rock into the water, and there is no chance he had ever skipped a rock. It seems to me that, even if you are selling a stay at a motel chain, the most important part of “acting” when skipping a rock is being able to skip a rock. I don’t think this guy, with zero lines, was THAT good at being a dad that they couldn’t have found someone who could skip a rock.