It's true that sometimes you just can't win due to leavers and such. However, you usually can win by simply being good enough. This does not only mean carrying your team, but also coordinating it, including getting your teammates to cooperate. This is a team based game, so these things are part of the skills of a good player. Most people don't realize this. Not to mention the fact that if you have a coordinated team of players you know and with whom you can communicate via voicechat, for example Skype, you will do much better than if you just randomly soloqueue. Another thing is that this is a videogame. Take it less seriously, stop raging at everyone, and you'll enjoy it much more, and will consequently start doing better, as well. Not to mention that teammates react much better to kind words than to rage. I have turned around so many losing games simply by motivating my teammates. It may sound like hippie bullshit, but it works wonders.