I think people are too focused on their stats.
I see this a lot in discussions when people talk about how good they are. They point out their KDA, their cs/min, damage or whatever else.
The problem is, that having good stats does not inherently win you games. Your enemy's nexus does not explode if you have 0 deaths every game, or if you get 10 cs/min, or if you get a bunch of kills.
If you're an ADC, and get 10 cs/min - does it matter if you don't know how to properly teamfight and can't get your auto attacks in? Does it matter that you have so much CS, when the enemy ADC with 5 cs/min can still out-dps you in the teamfight or pose more of a threat? Or if you don't take the opportunities for finishing their main carries by playing up/aggressive? I don't think it does.
If you're a jungler, get a bunch of ganks off and a bunch of kills, does it matter if you create no pressure and continue to farm your jungle? Let the enemy jungler scale up or gank your winning lanes? Aren't there for the important moments when your team needs you? I don't think it does.
I feel like having good CS and getting kills are a good step in increasing your ability to carry - but that's just it - if you don't know how to carry a game or use those advantages to get objectives, then it doesn't matter.
There are far too many elements to this game which allow you to carry a game. Reading your enemies and reading your team mates is very important.
TL;DR: Being a good* player means you will have good stats. However, having good stats doesn't necessarily make you a good player.
*good player: better than your elo.