I love this question, because on any given day I could give you a different answer!
Right now, I would say my greatest weakness is not giving enough credence to a players stats and not adjusting when they do something that should tell me I'm in a bad spot. For example, playing a tournament I had a player two to my left that had insanely nitty stats, something like VPIP: 10, PFR: 3, 3-bet: 2 over more than 500 hands. I'm thinking "great, I can steal this guys blinds all day long!". I get a few opportunities to steal the blinds which I duly do with any two cards and take them down.
A few orbits later I wake up with TT on the button. Effective stacks are ~50BB's. There's one limper in front so I raise to 4BB. SB folds and the super nit in the BB 3-Bets me to around 12BB's. The limper folds and I insta-call with my TT.
The flop is a beautiful 7-5-2 rainbow. Doesn't get better than that with TT, right? The nit bets on the small side, something like 8 or 9BB's and I thinking "Ha! You're trying to fight back against my stealing." I shove for about 40BB's, I have him covered by 3 or 4BB's. He snap calls and turns over AA. Board bricks out and I'm crippled.
Afterwards it was obvious how strong he was. He has pretty much the tightest stats I've ever seen and 3-Bets 1 in 50 times, or basically only when he has AA or KK. As soon as he 3-bet, I should have been folding quicker than I can say "I'm crushed" and got the hell out of the way.
Against someone with reasonable stats, I quite like my play and will often get called by a 7 or worse and will often get over cards and straight draws to fold, which I'm more than happy with.
Anyways...pay attention to stats, otherwise, what's the point in having them?