What are the factors affecting performance of human in playing computer games

There are a lot of variables that can affect the performance of a player. The most obvious one is the capacity of the computer/internet of the player. If those aren't on par with the minimum requirements for the game, you will get errors, have input lag and possibly ruin the game not only for yourself, but for the other players you are connected with.
Now, for the human factors influencing performance, you have several:

Fatigue - Depending on your state, you might be slow to react, have low awareness, get distracted/zone out easily and just plain not pay attention.

Hunger - Playing when hungry is not a good idea. You will not think 100% on the game and you might even be tempted to play more aggressively/go tilt.

Temperature - always keep your hands moving by micro-ing your keys, moving your cross-hair, etc. Having cold hands is bad.

There are many more factors you could think of but those are the most obvious ones.