What is the Dunning-Kruger Effect
It says that someone, who is unskilled will rate his skill too high, because he doesn't see his own mistakes. He also fails to recognize a higher level of skill. Wikipedia gives a detailed explanation.
Don't Blame Others, Concentrate on your Mistakes
When I learned about Dunning-Kruger I found it fits really well with the attitude of some players in League. Everyone knows these kind of players, who flame their team while loosing their own lane. I often see people who loose lane hard and then blame it on the jungler cause the enemy jungler ganked X times and their jungler didn't gank. They don't see that its their own mistake of not warding, overextending or going too aggressive. According to Dunning Kruger this happens because they do not know their mistakes. If they were, they would not make them.
Look at Others to Learn
The problem with league and what leads to this kind of attitude is, that you don't see what the other players are doing better than you. If you would see it and know why they do it you would be at their skill level, because thats the difference between League and other games. The mechanics are only one little part of the game. The rest is strategy. If you watch a stream, where someone is playing adc and keeps denying the enemy adc last hits by watching his own minions hp, it looks just like random auto attacks for someone who isn't using that technique.
What this means for your attitude towards your play style and your opinion about your teammates is, that if they are at your rating and you see a lot of mistakes by them try to find out what they are doing good, because they are at your rating for a reason.
For all the guys watching a lot of streams you should always ask yourself why the streamer does something. You don't get better just by looking at what he does.