The first major challenge about this is, to admit that enemy outplayed you. Most of the players don't do that. They will whine in all chat, that the enemy only plays noob-champions, that all of the enemy team's champions are completly overpowered. And when they get perfectly outplayed in a situation where they should definetly have won a fight "reported for scripting", "gg rito, we've got a smurf on the enemy team"
It is almost standard to look down upon the enemy and never admit that they might be good, maybe even better at the game than you.
The second challenge is, to see your own mistakes. Of course it's easy to blame your team for the enemy who is fed. But a lot of times there are also a lot of mistakes you've made in the game.
This does not apply to all games. There are games where you are the best player in the match, you perform outstanding but still can't carry.
And if you think back of games you lost: You'll remember these games more often than other games you lost, because of strong emotions (frustration) attached to these memories. Whereas you'll quite fast forget about that one game where you got completely outclassed by your lane opponent.
It should be seen as the third challenge. To put the games you lost due to your team and other looses in the right proportion. Don't just rely on your memorie, but be honest with yourself and go through you match history. Don't just ignore the looses that were not solemnly because of your teammates.
(There are players who can overcome these challenges and they probably won't share your feeling about only loosing due to your team. And they are mandatory for players who are dead serious about climbing)
In the end, it's all about how you perceive it...