Like someone said earlier, being a tank or a healer is a relatively thankless job. If somebody besides the Tank dies, then clearly it's the Tanks fault, if the Tank dies then clearly it's the healers fault, while the DPS's get to be the heroes of the story. Doesn't matter if the DPS keeps stealing agro or the Tank runs off away from the healer, it's clearly their job to be right beside them protecting them.
You can only take so much before you wander off. The only GOOD thing about being a tank is usually there's a short wait time for GF because no one else wants to tank for it.