I've come to believe that platinum is the real elo hell.
I think it's right at the point where people get a big head and THINK they are so good, that they can now ignore all basic mechanics of the game. The majority of people just absolutely lose their minds and all knowledge of the game when they enter Plat. They stop warding, they start face-checking again like they did in bronze, and they lose their lane almost every single game.
If you aren't prepared to be able to 1v5 the enemy team-- EVERY GAME-- and just pray that they don't feed that Kalista or Jinx 10 kills in the first 10 minutes, you wont last.