Im Quitting Based on What I Read on Riot's Offical Matchmaking Philosophy...
This is why is so hard to climb and you go on losing streaks. I decided to buckle down and get to gold, so I am only playing champions where I really excel. I start doing really well and win my lane in every game. Then after I win about 5-6 games, I going on a crazy losing streak and I was always curious why this happenend. I always thought you were matched based on MMR so when you join a game you would theoretically have a 50% chance of winning, but increase those odds if you do well. That is not the case.
"Each player is assigned a number that represents his skill level (MMR) which is determined by the outcomes of his previous games. With this matchmaking rating, the system will attempt to assemble two teams as fairly as possible to create a game wherein both teams have an equal chance of winning."
https://support.riotgames.com/hc/en-us/articles/201752954-Matchmaking-Guide
This means if you are doing really well at an individual level they will place you on a team with players that haven't been doing as well; therefore, decreasing your chance of success. Instead of placing you on a team with a 50% of getting players with similar skills, they place you on a team with worse skills than you because you have been playing well.
This is why is so damn hard to rank up.