We've all had those games. You beat your lane opponent, kill him 5 times by 10 minutes, you're up 100 cs and a tower, and have two major items while he is stuck with boots and 2 Doran's Blades. You feel confident in this game. But then the mid and jungler start camping you, your bot lane gets double killed three times in a row, you lose two dragons and your lane opponent catches up. You might still be able to beat him, but there is no way you'd be able to handle the 12/0/4 Vayne who has a Bloodthirster, Mercurial Scimitar, Infinity Edge and Phantom Dancer before 17 minutes. So you /ff, shrug your shoulders and say "bot fed, nothing I could do."

That isn't true. You could have done something. Maybe it wasn't entirely your fault that you lost, but you could have, and should have, helped.

I've seen players throw games because they want to make themselves feel good. I've seen players win games because they refuse to get pissed and /ff. Something hugely important to realize is that your success and your teams success are linked, but they aren't the same. You can kill the enemy Karthus 7 times as LeBlanc, but if you don't help other lanes, you'll be absolutely useless as the game drags on. Or you could be the Karthus, and help win the game with your ult despite losing lane.

The point I'm getting towards is simple: if you're ahead, utilize that advantage to get your team ahead. If you're ahead and the rest of your team is falling behind, you have a few options:

• Splitpush and try to occupy as many enemies as possible while taking as many towers as possible. The global gold you'll grant to your team might help you counter snowball.
  
• Try to take objectives. I've learned that emphasizing objectives can turn lost games into won ones. Especially if you're playing an assassin like Lee Sin, pick one or two of them off then rush to Dragon, or Baron. Even stealing away their buffs cam make a huge difference.
  
• Roam. If you pick up a few kills at top lane, gank mid. Or try to teleport bot lane and gank. Snowball as many lanes as possible and try not to throw, and you should be solid.

If you're behind and the rest of your team is doing alright/good, call your mias. Games can go sour quickly if one person is allowed to roam freely and help other lanes. Other than that, try to farm and look for opportunities to roam yourself.

There are unwinnable games. I'm not denying that. There are games where you try for the perfect roam and bot lane ends in a quadra kill, with your jungler and laners going down with you. And those games suck. But if "every game I get stuck with feeders and noobs" is your mantra, you aren't playing League of Legends correctly. It's a team game, first and foremost. And you win when your team wins, not just when you do well in lane.