I think saying things like that is also meant to be inspiring. Like when you tell all the kids on a hockey team that they're great and they're gonna kick ass out on the ice, but you know who they're about to play and they don't stand a chance. But who knows, maybe telling them they're great will get one or two of them to dream about being a future hockey hero, and they'll get out on the ice and really kick some ass for once - make that extra pass, hit the net for a shot, or hold off on that big, useless, cross-check to the head that would put them in the sin bin for 5 minutes.
If the kids can dream, so can you, right?
Maybe you'll inspire those bad apples to be great.