Practice doesn't help?

When Playing Halo (which I play a lot) I always imagine that I'm going to do better....this time. Hey, I've worked on my BR, I've practiced using the SpLazer, sniper, and rockets, I know the maps and where the weapons spawn, Hiding spots, even map strategies. I feel I have the knowledge to be able to compete, but this is not the case. I almost always end up negative and even those rare time I end up positive its + 1...how sad.

Here is an example (social slayer for that matter): I start off good on High Ground grab the SpLazer and attempt to go to work. I take out the Ghost, and get a couple of kills..I even make my way to a spree, but then it happens...Death after death after death. A complete embarrassment. Even after starting with a spree I go negative and I'm give them thier last three kills. Sad Face...