That happens to everyone at some point. That game where you should have won, but you didn't. How two lanes did well, but one didn't. Your team made one mistake, and it costed the game. Yes, this kind of game happens to everyone. Not everyone is a perfect player. Sometimes we have a bad game. If you truly did well, it will reflect on your match history, or your average with that champion. If you see them doing something wrong that you know is an easy fix, just nicely tell them. No one is going to get better if they don't know what they are doing is wrong. Believe me, everyone feels like they don't deserve to be in the league they are in at some point. Just keep trying, you'll win eventually!