Why are dogs so good at guilt trips?

If you are a dog owner yourself, or if you know someone who loves their dog, and I mean really loves their dog, then you've probably been a witness of the classic "puppy eyes" guilt trip that pups play when they know you are leaving the house without them. My maltipom (half maltese/half pomeranian) Petrie often gives me those melt-your-heart eyes, with his own added sass, among dozens of other expressions he's mastered in which he uses to his advantage.

Here is a picture of Petrie's routine for when I am leaving without him:

At the top of all those stairs, he looks just like a little seal pup to me. When I am getting ready to leave, I always make sure to give him a little kiss and pet goodbye. As I descend downstairs, he does not follow, as if walking me out to the door and saying goodbye there would just be too much to bare. 

Tell me that saying goodbye to that sad little face isn't a valid reason to make you wanna hurry up and get what you need to get done, done, so that you can return home and be welcomed back by the happiest bundle of joy!

This was the joyful welcoming back I received from Petrie after being gone for just 3 days. :)