I guess whether a bullet would knock you on your backside depends on what size it was and what it hit. If it went straight through you, then perhaps it wouldn't as its energy loss wouldn't be into your body; that said the hole that it left would probably mean your appetite for staying stood up would be somewhat diminished.
car doors aren't bullet proof tyres don't screech on dirt roads cars don't explode in mid air when going over a cliff cars with manual gearboxes don't go faster in a race if you change down a gear oh and there is no beep beep when locking a car