Dont you hate it when?

Ok, so im not trying to brag or anything, but i think of myself as pretty good at any shooting games (cod, halo, l4d2 ect.) i always find that i go like a crazy amount possitive and we still lose by like 10 kills. I just wonder if its just me thats gets this often, or if other people experience the extream noobs that go like -15 .

Im also looking for anyone thats like decent at halo 3 to play with, i just got back into that game lol if so pm me ur gt