The best thing David can think of as a comparison is tapping on the napkin.

"Skating in a managed indoor rink and skating outside are likely as different as a sketch on proper paper and on a napkin. In a rink things are smooth, managed, the bring out Zambonis to smooth the ice as it gets scuffed and worn and chipped. Outside? The ice is only as smooth as nature freezes it. You have to learn to read it, have to anticipate bumps. Have to be thinking ahead and far more attentive."

It's a mental challenge. And it seems o much more forbidden, because there is a dangerous edge to it.