As someone who works full time and attends classes, I don't know every nuance of every fight. I always say "1st time here", but players do not always offer up tips, so I end up making stupid mistakes that could have been avoided.

Also, as a rogue, sometimes the tank pulls too fast for me to play effectively. Stealth has a cooldown and if the tank doesn't hesitate once in a while, I can't use half of my stealth-dependent abilities without wasting a vanish. Starting a fight in stealth is essential for some rogue specs.