My weaknesses in chess is I am an argressive person and I want to win fast as I could and If I am thinking a lot or If I am not concentrating to the game, I am sure my play will be lose.
I would agree with some of the early posters - moving too fast, and moving reactively as opposed to actively - when I play chess based solely on what the other guy's threats are, how boring is that?? And yet it's what I end up doing fairly often...