Like I said, luck. I'd rather figure a buck's daily routine out than rely on him making a mistake and blundering past me.
That being said, I kill bucks every year during the rut. Usually ones that weren't on my hit list. It's fun to meet new faces.
Why is it that you think everyone that kills a buck during the rut is luck? Some of us do it on purpose with identified target animals first time in - don't think that is luck?