There is a difference...
... between knowledge of the game and skill at the game, and I wish people would learn the difference. I'll use the guy I had a few games ago as a shining example. We were having a rough go of it and I gave him some tactical advice. I told him he was targeting the wrong enemy (the tank), and that he was pursuing kills too aggressively when we were behind.
His response: "stfu you rush lord dom on akali, your too stupid to give me advice"
I replied that I have a rather good win rate on Akali, for my skill level, building AD. That my decision was a tactical choice. They had two tanks, and Akali scales hybrid. As I always like to have at least one AD item on Akali anyway, I decided to make it Lord Dominik's Regards, so I could do a little more burst damage to the tanks when they ganked me. They were roaming quite actively. As I can escape most any gank with Akali, I figured being able to hurt them before they left would help the team at large.
His response: "yeah, [you have a good win rate] in Bronze"
Yes, I said, in Bronze. Where I am. Where he is. The tier that suits my skill level. Where he was as well, I pointed out. I expected him to say he was a smurf, but I got the other cookie-cutter response: "because noobs and feeders like you keep holding me back"
This comment said it all. The reason he was so aggressive, the reason he never pushed objectives, the reason he felt so superior despite being in bronze, same as me... was because he was all about the solo carries. The KDA was all that mattered to him. "I have a better KDA than this guy, therefore I am better at the game and he has nothing useful to tell me."
After the game, curious, I looked him up and I found something interesting.
https://i.imgur.com/jiIC0b4.png
I notice a major discrepancy between two facets of our profiles:
1. KDA. Without a doubt, his KDA tends to be higher than mine, and considerably so. At least if recent games are any indicator. And this is perfectly logical. My KDA generally hovers around 1:1, sometimes lower. Mechanically, I'm not the best player. However...
2. Win Rate. Notice the difference between our respective win rates in recent games. And yes, I made sure to update on both sides before I committed to comparisons. Percentage-wise, our win rates actually show a much greater discrepancy than our KDAs.
Now what does this suggest? To many, I'm sure, it says "Oh. You get carried a lot." But that's not statistically logical. A sample of 20 games is pretty significant, and my win rate has remained pretty steady throughout my life on League. I usually stick around 50%, closer to the mid 60's with the few champions I'm very comfortable with. With an average KDA of 1:1, I'd say that's about right, wouldn't you? 50:50 equates to 1:1. My KDA matches my win rate, as it were. If I got carried "a lot", one would suspect my average KDA would be lower than my average win rate.
In short, I have a logical impact on the game. I don't carry, I don't get carried. I contribute. Sometimes I win, sometimes I lose. I'm average.
Let's contrast this to our verbose buddy here. His average KDA is rather higher than mine. It's by no means an amazing KDA, objectively speaking, but it's certainly better than my average. So why does he lose so often? His claim was that feeders and noobs hold him back. Being in the same tier of competition, though, over the course of the sample... Wouldn't I have gotten, on average, as many feeders and noobs as he did? So why, when he's such a statistically superior player, does he lose so much more often than I do? Logically speaking, that's not the issue here (unless he has incredibly poor luck, but we had neither feeders nor noobs in that game and he claimed we did, so more likely, he's full of it).
And now we come to my theory: I win more games because I am more concerned about winning the game. What do I mean by that? I mean that I don't care what my KDA looks like. I don't care if I go 0/20, as long as my deaths helped us win the game. A lot of my deaths come from saving two or more teammates, skirmishing so we can grab dragon or baron, leading the other team on a chase while my teammates are down and our base is exposed, and so on. I die a lot, but they're generally (not always!) calculated deaths.
This fellow, at least in the game we played together, generally died because he got overwhelmed in a teamfight. Never once did he tank for teammates who were fleeing (interestingly enough, he was a tank...). Never once did he zone for an objective. He rarely even pushed turrets. Generally, he'd just chase every enemy player that appeared on the map, the moment they appeared. He'd literally run from top to bot because a lone enemy popped up on the map. And he's far from the only player I've seen do this. Interestingly, those who play like this often share this mentality of "I lose because [of something my teammates do or don't do]."
The point of my post is this: TACTICAL knowledge of the game is preferable to MECHANICAL knowledge of the game. Think of it this way. You take the best sport marksman in the world and put him in a fireteam in an active combat situation, zero military training. See how effective he is. Chances are, he's going to bumble around between cover, never knowing where to fire, possibly even missing most of his shots. By contrast, you drill some good, old fashioned soldiering into any common farm boy, and he can help his squad take ground like he was born for it.
Being aware of what your opponents are doing, knowing the right items for the situation, knowing how your champion can stretch the mold when the odds are stacked against you or you're counterpicked, knowing who to protect and who to target, knowing when to fight and when to get objectives... That's what's going to win you most of your games. If you come in with the mechanical skills of a pro and the mentality of a guy playing a single-player beat-'em-up, your games aren't going to go as well as you think they should. And when they don't, you're likely to blame it on our teammates, because how can it be your fault when you're playing so well? That's going to lead to division and irritation, which is going to make your game even worse.
Instead of wondering how someone so skilled can lose so many games, you might want to realize that knowledge and tactical sense are game skills as well, and you're not as skilled as you think. Hit the books and change your way of thinking, and you're probably going to start winning more often.

on
. You build
. You build
. You build
on
.
- and until they do, they allow me to sustain even if the enemy has range on me.
,
and 

for the CC or the Magic Damage Threats, and
for the Physical Damage Threats. You need to be able to take damage for your teammates in order to be helpful as Illaoi.
.
These items give you health, damage, cooldown reduction and health regen.
. Illaoi is a self-healer thanks to her Tentacle Smash. If you landed a good Ultimate, you'd have so much Tentacles that you'd never die thanks to your insane amount of lifesteal from this item and her natural self-heal.
JUNGLE :
MID :
SUPPORT : 
, the 1v5 king if he's fed and will scale late game too.
, which means that all in all, their team is really squishy.
who can't add much to the fights.
.
- Armor + Health + Health Regen
... )