In all seriousness, I think most of what has been said here can be applied to three psychological issues: tunnel vision, going on tilt, and our ego.
Tunnel vision is where you get so focused on one thing and where you get so determined to do something that you ignore everything else. It doesn't matter that to catch the 10-health Shaco you have to tower dive the entire team, you do it. It doesn't matter if the enemy team is threatening you on the outside and pounding on you, you gotta finish baron.
Going on tilt is a phrase used when you mess up, and a fight-or-flight response of sorts is activated. Since this is a video game, we don't know how to act, and get apprehensive. As a result, we rage, blame, and do stupid things in an attempt to feel better, when really it helps no one. It's also why you shouldn't go into a game if you're tired, angry or depressed.
When I first got into Ranked, I won the first five matches and got into 1350 elo (back before divisions). I then summarily lost the next ten or so games because I decided to play while I was tired, on a champion that I needed to be on point for. I stayed around 1100 elo for months because "my teammates were bad" and I was in "elo hell." Since that I had gotten into 1350 elo, I had an overly inflated sense of how good I actually was, and as a result, kept getting frustrated at the system, even though it was working the way it was supposed to. I wasn't ready for a higher tier yet. Only two weeks ago did I finally get into Gold after almost a year of Ranked queue.
When you feel any of these happening, then I would suggest you stop playing before you get on a horrible losing streak. Remember, your teammates might not be the best players, but neither are you. You will make mistakes, too. Learning to recognize what those mistakes are can be hard. All of the posts above me give good information about the mechanical aspect. Focus on improving mistakes, and you'll be on your way.