Confused about pet evolution

narcisse

Pre-Searing Cadet

Join Date: May 2006

I just raised a pet to level 11 while never attacking anything and also preventing my pet from taking any damage at all 99% of the time, and he still ended up Playful. Is there something else I'm missing that I need to do to make him Aggressive? Is there really a noticeable difference between Hearty and Dire? Should I even bother trying to raise another pet? Thanks for any help