Well, I've been playing since Vanilla, and not to sound arrogant, but I consider myself a pretty good player (admittedly, I didn't really get "good" until Wrath). I feel like I know my stuff pretty well, and I'm constantly researching strats, builds, and just anything that can help me play better. When it comes to DPS, I'm perfectly fine; even on the rare occasion that we managed to make it to a new boss before I had the chance to research it, I can always keep a level head.
When it comes to tanking, however, it's a totally different story. I've been just farming Heroics, but I always feel on-edge the entire time. It's not that I have a hard time tanking it -- I'm not well-geared yet, but haven't died yet, short of someone else wiping us -- but I just always feel incredibly stressed-out the entire time. Am I pulling fast enough? Too fast? Am I just not taking any damage, or is the healer having to work overtime to keep me up? It doesn't matter if they tell me I'm doing fine, I'm always just incredibly nervous when I'm tanking.
Have any of you ever had that problem? If so, did you ever overcome it? Or, for whatever reason, am I just not cut out to be a tank?