Well there's a lot of it going on. Process of elimination.
Here's a productive explanation. Let's say you plan to fish the upper Gravois during the event, so you prefish in Indian cr., Soap cr., Mill cr., just to get a feel for how the fish are biting and what kinda areas the bigger ones seem to be hanging out around. So you've done 2 things....you learned a few things about what kinda spots you need to concentrate on, AND you sore-mouthed some fish in OTHER creeks, making it harder for the poor basturds that fish there to catch any.
I'm guessing that none of the 200+ guys in the Gravois today will be in the Gravois come Saturday-Sunday.