Before developing a sense of object permanence, a child believes that if he or she cannot see an object, it must not exist. That means that when mom leaves, she is gone forever. If food is taken away, it no longer exists. And if the child cannot see the second season of Firefly, it must be because one was never made. Hmm.
Dogs have some ability to understand object permanence, but not as much as humans. However, the dog in A Dog's Purpose understands complex theories of reincarnation, so maybe it's no surprise that object permanence is easy for him to understand. That doesn't mean it's easy for him to deal with the fact that when some people leave him, they are gone forever. In fact, it may be that small sense of object permanence that makes it harder for a dog to cope with abandonment sometimes; dogs know their favorite person is out there somewhere, but they don't know if that person will ever return.
Questions About Abandonment
How does the dog feel after being abandoned by his mother in his first life?
Which humans betray the dog's trust by abandoning him? How does he feel about these people?
When Ethan leaves for college, how does the dog feel? Does he feel abandoned? Does he forgive Ethan?
Chew on This
The dog escapes his cage in his second life without giving any thought to the fact that he is abandoning his dog mother. In the dog world, it's every dog for himself.
The dog learns to accept that human lives are greater and more complicated than his own. He also learns to accept that humans come and go, though that doesn't necessarily mean that they are abandoning him.