Some games (Quick matches, but happened with Hero league as well) you're paired with a few newbies and set against some skilled players. There are no comebacks from that, really.
The problem is that a skilled player will contribute to team fights more AND follow objectives better. When games turn like that, they're just not enjoyable.
Plus, the only skilled player by your side will most probably start raging against "noobs", with detrimental effects.