Opportunity for Improvement

My 11 years old daughter and her friend were making a list of kids from their school and assigning percentage points for how much they (daughter and friend) liked them. Mom and Dad said that it might not be such a good idea as someone with a low score might see the list and have their feelings hurt. Before my daughter could  respond, her 20 years old sister piped in that it would be OK, as they could see where they stand and where they could improve. They all nodded in agreement and continued working on the list. 

My youngest daughter at age 5 had a similar list. It started one day when she created a rather nice piece of art and presented it to mom and dad. We, of course, encouraged her, to her delight, through praise. Later, however, the artwork took a sinister turn. When scolded by her mother, she dashed off to her room to pout. Then, about 20 minutes later, with leveled angry eyes, she returned with the artwork that was the object of so much praise earlier and asked mom, displaying it as she did, "Do you like it?". "Of course we do honey", mom said. "Do you really like it?" she asked again. "Yes, I really do", mom said again. And with that, my daughter bared all her teeth and ripped the picture to shreds yelling, "That's what you get when you make me angry"! The shocked looked on all of our faces was justification and encouragement. A few days later, my 5 years old upped the ante and created a long piece of art that included drawings of the entire family. When angered, she'd slowly, calmly rip a family member from the picture with each infraction.
I just can't come up with a moral or lesson learned from this experience.