Everything Goes Great... Until Late Game
So I'm playing in unranked, and I ping the target because they're exposed and we can quickly turn a 5 v 5 into a 5 v 4. But the team decides to go after the tank, who's for some reason buried in the teamfight. The exposed champion quickly gets a skillshot off the side because we didn't kill her, and suddenly she's pentakilling our team, because our team decides my ping is worth nothing. Another case: Yi decides he's going to 1 v 5 the enemy team. Unsurprisingly, he gets killed and the teamfight becomes a 4 v 5 killfest.
I've played so many games where we get such a good laning phase, and their team is in no way set up for late game, but it all goes wrong in a teamfight because of stupid teammates.