For me personally... I have issues with stress, and I find melee in general and tanking in particular very stressful. I am uncomfortable having my field of view limited by large mobs. I much prefer to heal at range where I have a larger field of view and can see mechanics incoming to avoid. But even healing is more stressful in FFXIV than most other mmo's cause I'm expected to dps as well... and I KNOW I've caused wipes because of switching into cleric stance at the wrong moment.

I tried doing the Thordan minstrel quest. I told the group I had never done it beyond the initial story mode and no one would explain the tactics but they were sure quick to let me and the other healer know we needed to dps. Eventually after a few wipes I saw how the mechanics worked and when it would be safe for me to dps but we still had to abandon the duty because we kept wiping.

I can't even imagine going into that experience as a tank.