Don't use Duty Finder to practice tanking. You can't trust that complete strangers will be patient or even care whether you are trying to become a decent player with that class. Personally, I stop and take time to explain and teach new tanks when I can, when I can't I wish them luck and move on before it becomes a painful run. If you are going to learn, the best people to do it with are FC members that you are comfortable with, or RL friends. Patience is not inherent in MMO gaming and never will be, accept that and work around it.