I can't say it around enough, how important being positive, calm and collective in game is actually important. I mean i just had a game where one player gave up after one of our lanes kept being ganked over and over, because they were way ahead than our enemy team.
The player kept saying it's over, kept surrendering. But the rest of us weren't about to give in just yet. I just said keep calm we got this, it's ranked we have one fed player. The enemy team was 3 dragons and 1 baron up on us. We evened the dragon score and took 2 barons. And after 40 minutes of getting our sh*t together(xD), after countless of teamfights and skirmishes we won. It was a great feeling. Even the player giving up rallied with us and we pulled it off.
Really guys and girls being calm and talking positive in team chat, can and will win you games, turn around team advantages.
You will see the difference yourselfs.