It's generally a matter of: your play weakness aren't the same as theirs, so you see theirs in glaring light while you're blind to your own.
HOWEVER, I will say this: queue'ing up with 4 people usually sucks massive balls. For some reason, that random never seems to have any idea what they're doing, and they're always a half-step from raging. I've taken to calling this "picking up a Hufflepuff" whenever we have the misfortune of only 4 friends on at once. It's like:
"Okay. We won a teamfight. Let's go grab <Objective X>."
ping objective
"Sounds like a plan. Wait, where's <Random Player> going?"
"Looks like he's going to kill wolves. Again. He can see our pings, right?"