The existence of ELO Hell
I've played with a bona-fide diamond player smurfing in bronze (me i am gold 5 on main). We lost 6 games in a row in bronze 3. In every game we both did good he had 2x champ damage of other players and usually had at least 18 kills. One game he had 28 kills and we still lost. In every instance, our remaining 3 teammates could not figure out how to even safe farm let alone take objectives while we were annihilating the enemy team. Eventually they caught up to us and we lost the teamfight. ELO Hell is real.