I REALLY dont get it

[JetLi'sFearless]

in movies when a guy htis the other in the gut even if he doesnt even use his shoulder pwoer and turn with the punch and just throws an arm punch, the guy who hits the other guy always drops him. WHen I did a [proper sucker straight right to the guys gut, and another time kneed him there while grabbing his neck with my opposite arm and his arm he just started fighting me. Why wont they drop when i hit them there? is it casue IM not hitting them in the solar plex but too low? or is it that the adrenaline they have makes them not feel it? Heck even zidane dropped a guy to the ground with a headbutt to the chest and I cant even do it with a perfect right to a freshman-sophmore )possibly junior but i doubt it) high school kid for some reason.