Been tanking for around 8 years, and Warrior is my main (switched from Paladin). Tanking in general is actually fairly relaxing. Compared to when I DPS or Heal...Tanking is very easy from a job standpoint.

Where tanking get's complex and stressful is:
1. Boss Positioning (raiding specific). Standing still and keeping the boss situated correctly to prevent frontal cleaves/tankbusters/positionals for DPS/centered in the arena. This requires situational awareness, understanding ground markers, understanding your minimap. This comes easier the more you do it, and helps when raiding.

2. Tank Swaps. Not around how the swaps are done...but making sure your co-tank understands when to provoke/shirk. Example: PUG'ed Hades EX once. The ice/fire add phase you need to grab hate on one of the adds AFTER you see your debuff. Ice debuff grabs the fire add. Vice Versa. I had a co-tank that just started DPSing one of the adds BEFORE the debuff appeared...50/50 chance they were right, but this time they were wrong. Now they have hate on the wrong add, and I need to voke it off of them wasting my provoke for the tank swap when they swap the debuff right after the. To add insult to injury the co-tank should have shield lobed, and pull the add...but RAN UPTO the add to get hate, and passed it near me....the adds link....both tanks die. Now pugging is mixed bag, shame on me for assuming the tank knew how to handle that phase.

3. Battle Knowledge. This goes for ALL roles, but Tanks pretty much have to know EVERY part of a battle/boss more then any role (imo). Where to stand, north/south/east/west...sometimes in reverse when MTing (east is west and west is east),
Boss percentages for phase changes, adds, sneak attacks you may not see. (eden fulmination horses).
I find myself calling out fights MUCH more when on my tank then on DPS or healer.
Cast bar attacks and knowing what each one means. This isn't to say that you will never know a fight...it just takes practice as most extreme/savage are extremely scripted. Seat of Sacrifice is exempt due to it's 2nd phase RNG for 4 major mechanics. One of the better designed Extremes...if not the best.

4. Mitigation judgement. When to mitigate and which skill to use. Example: My HP is high...use Raw Intuition. Tank buster incoming....vengeance and/or with low HP add Thrill of Battle. If I have a TBN from co-tank with tank buster coming in...just pop rampart. Mitigation is a tanks gameplay vs. DPS positionals/healers...well healing/DPS buttons.

Tanking isn't scary....being scolded for not understanding fight mechanics or where to stand is. That's where most the tanxiety comes from. Just learn to get comfortable with the fight.