Well, gentlemen, you were right. I was lucky (and my mentor was a really experienced guy who knew the area better than his backyard) and a deer showed up. Actually, not 1 deer but 7 (2 bucks).
I missed. There's a huge difference between shooting a target and a moving deer. And it went very rapid. One moment you disbelieve you'd even see any deer. And then there's full-throttle motion and the deer is gone.
I guess, there's a lesson for me nonetheless. Would I spend more time sighting my shotgun and learning to snap-shoot it (by taking it to a sporting clay course maybe) and would I practice at least a little bit of a moving target shooting, I'd be eating venison roast instead of rice.
I guess I've got some time before the gun deer season opening day here in WI!