As you view the higher ranks you see something in common.
Less mistakes.
The lower the elo, the more mistakes.
The higher the elo, the less mistakes.
When you watch the lcs you see very few deaths, thats because they make less mistakes and play smarter, safer, etc. in that game.
For every death there was a mistake made on your part or someones part.
I get it, some deaths you thought youd rely on your teammate and he screws you because hes too scared or didnt have the map awareness, or whatever and doesnt follow up or help you, and you die for it. It happens, but most if not all deaths will be a mistake you made.
If you care for it, record your games, and rewatch it and the games you think you played well, rewatch em and see how you really played. Youll soon realize how many mistakes youve made.
You may not be punished for all your mistakes, but im sure some mistake/lesson will be learnt per game. Whether its not having vision, overextending, awkward positioning, etc.
So basically just record your games you play seriously in, and rewatch them to see what mistakes youve made.