This is a common misconception, often caused by seeing a winstreak end because of something you could not control, and enabled by a misunderstanding of matchmaking.
If you win a game, then your MMR will go up a little, and the game will match you around that new MMR. Your opponents and teammates will be better. If you go on a winstreak, then your MMR will go up a little more each time than the last, eventually putting you with opponents and teammates around your real skill level. Here’s why this feels like the cards are stacked against you.
Your winstreak might have had a little luck, or not, but regardless your skill was behind most of it. But each win makes your opponents a little better, meaning that you get fed less easily and have a harder time pushing your lead. Eventually, they’ll be so hard that getting fed will be a 50/50, and so will pushing your lead. But because it’s gradual you won’t notice until someone on your team inevitably trolls or feeds. And then you remember some half-heard thing about 50% winrate and say, “Ah, see, it wasn’t my fault. I could have climbed further but the game held me back.”
And so you feel a little sorry for yourself. Which is fine. I do too, and sometimes whine to a friend, if ‘muh tee-yum’ throws a match. But then I remind myself that if I were much lower than I deserved, then odds are I could have carried the game before it got out of hand. And besides, if even if I am near my true rank, then the trolls will be on the other team half the time anyway.