Some people don't really understand shit about roles. We've got a tank! No we don't, he doesn't tank. Like I'm playing Soldier and Reinhardt is ahead and there's this turret we need to break. So I start firing and suddenly the dude goes somewhere else with his shield, probably to try kill some Tracer. We couldn't get past that turret. It was sad.
Or I'm tanking this choke point with my shield and people are behind me and I want to break in and they are making no further action. My shield breaks and I go for cover. When it is refilled, I say: Shit, people are not fucking using my cover for anything. So I cross the choke point and go to my left charging and ulting. I kill half the team, we've done it! Or maybe not. My team is still at the choke point, even though there's no choke anymore, they haven't stepped in, so I have to run back to the former position. They just wanted to shoot safe from the choke point, it seems.
Then, we get best random team. I block 18k damage, and Mercy heals and revives like crazy, and people stay behind me and shoot things while others go sideways to kill those trying to burst my shield. What we did? Nothing but play our roles. Yeah, it's tempting to go crush things with your hammer from the backline, but you probably are better covering the dwarf while he builds his turret.