User blog comment:N00bpl0x/Do others have this problem too?/@comment-5761259-20130601080207

This could be one of two things. The first, as you said, is team comp. If they have really good wave clear, or other ways to prevent you from pushing, then they can eventually just out push you. You said even team fights, which means I'm disregarding champs like amumu or katarina being in the game or effecive.

The other is that they had better objective control. Did they take lots of dragons, barons or towers? If so, they had more gold than you, and probably a slightly stronger fight over all. If they did have more towers, then I assume that they were simply out pushing you, which goes back to team comp. If they have one or two effective clears, and then two champs with high AD, then they could probably dunk towers quickly, meaning them coming out on top of a team fight would be better for them.

I actually thought of another thing that might have happened. Luck. Sometimes, there is a bad engagement, they come out on top, and suddenly they have your entire mid lane gone.