Okay, so i am going to premise this post with a little bit about my background. I've been playing league for about 6 years, mainly maining jungle and mid for the majority of those years and mostly hovering in the plat 2 to plat 1 area for at least 3 years of that time. However, last season, i managed to climb to diamond 3 (and dropped to d4 but we dont talk about that) after being hardstuck for many years. So, i can say i know a fair bit about some fundamental things about league of legends ranked.
This is my smurf account, where i started playing adc only to see how far i could get. Eventually, whether through tilt or bordem, i switched back to my main role and main champion (twisted fate) to see if i could get this account to diamond. One of my very first issues was, regardless of how well i did, or how well at least 1 person on my team did, i would lose games that should not be lost. The core problem was, players on my team, and occasionally the enemy team, would make some very interesting emotional plays. And why i say emotional plays its usual things like running into the entire team 1v5 out of anger or frustration, or something similar to that. Its usually pretty easy to tell when somebody is tilted and makes these plays, as these are things players in plat and diamond should not make. This happened for like a week straight. Constantly, people on my team would suffer from this problem. But then i realized, that not _actually_ my teammates, but rather myself. I suffered from this problem extensively, whether or not i realized it. I was definitely not conscious of this. What i would do, was unconsciously tilt myself, which would ripple through the team super quick. For example, lets say my jungle comes mid and dies to my laner, now im behind 300g and jungle has lost pressure. I would type something like "Are you crazy/stupid?", but regardless of this i would still stay positive about the game. But the damage is already done, now the jungler, who already knows what he did was a mistake, gets tilted from that comment, or ping, or whatever it is i do and now we have 1 tilted player. Lets say this player goes to another lane, tilted now, and makes another mistake, now my single comment has caused damage in 2 lanes. And now that lane is angry, and so is that player. Arguments break out and everybody is tilted and makes emotional plays and throws the game. Boom, just like that, that single comment i made about a misplay potentially ruined the entire game. Its even more interesting to notice, when this happens to me. Let's say i make a huge misplay, maybe miss a flash, or maybe lock in a red card instead of gold. I get flammed hard. Now i know what i did was a mistake, but this comment, even if i dont realize it, manages to subconsciously tilt my mind. I start making similar mistakes and getting flamed more. The frustration from arguing with my teammates, or with how bad i misplayed, will continue to cause me to misplay, and just add more to the fire, and eventually lose the game, and maybe tilt my teammates too to do similar things. This is, in my opinion, the single worst issue with ranked right now. People are not robots, and do experience frustration and let their emotions affect their gameplay drastically whether they know or not.
So maybe this might help players who have experienced a similar problem to the one i described above, but the number one thing i did to tackle this problem was to completely remove in-game chat. Not only would i not potentially get tilted from what teammates say, i would also not accidentally tilt my teammates. We must also keep in mind that 95% of tactics that can be pulled in-game can be conveyed by pings alone, so i knew communication would not be really an issue, and it actually hasnt. This actually, became such an efficient way to improve my gameplay. The instant i disabled in-game chat, i went from p4 15lp to p3 56lp in 1 day(after being stuck p4 for like 2 days). My play had improved and my mistakes were less frequent. Because regardless of what mistakes were being made by me or my teammates, i didnt have to interact with them in chat or recieve the flame from my teammates, which obviously made me more focused on the game and how i could win it. So definitely checkout the video on how to do this if you care, just saying this definately worked for me.
disable in-game chat = more focused gameplay and better winrate (at least for me)