"Group and we win"
I am tired of pointing this out. Literally every game I am in, literally everyone tries to force a teamfight, even when we have absolutely no business doing so, even when it's the dumbest thing we can do, even when there are a quintillion better things to do. Grouping is NOT an instant win condition at all times just because you think so! Because anything YOU can think applies just as much to the enemy team!
If your ADC is massively fed, yet you don't have any peeling power, guess who the enemy team is going to focus first? If you are nothing but ADCs and assassins and the enemy team has crowd stuns and crowd damage, guess what you shouldn't be doing?
Yet every game, the exact same thing happens EXACTLY as I predict down to the minute movements of individual champions, and no one can get it through their fucking skulls. Teamfights are not the absolute end all be all to this game, no matter how much you want it to be, no matter how much you want those pentakills. Sometimes grouping up loses more games than winning them.