What you don't want to see coming at you from astern.
No doubt about it, if you don't pay attention, you'll be sleeping with the fishes.
I'm continually surprised by all the numbskulls I encounter out on the water. I've got news for you guys, it's not virtual out there, stuff can kill you. So pull your face away from that smart phone for a second, and take a look around. Welcome to the real world, there isn't an app for that