A four year old child's wisdom: Why dogs do not live as long as people.

Being a veterinarian, I had been called to examine a ten-year-old
Irish Wolfhound named Belker. The dog's owners, Ron, his wife, Lisa, and their little boy, Shane, were all very attached to Belker and they were hoping for a miracle. I examined Belker and found he was dying of cancer. I told the family there were no miracles left for Belker, and offered to perform the euthanasia procedure for the old dog in their home.
As we made arrangements, Ron and Lisa told me they thought it would be good for the four-year-old Shane to observe the procedure. They felt as though Shane might learn something from the experience.
The next day, I felt the familiar catch in my throat as Belker's
family surrounded him. Shane seemed so calm, petting the old dog for the last time, that I wondered if he understood what was going on. Within a few minutes, Belker slipped peacefully away. The little boy seemed to accept Belker's transition without any difficulty or confusion.
We sat together for a while after Belker's death, wondering aloud
about the sad fact that animal lives are shorter than human lives. Shane,
who had been listening quietly, piped up, "I know why." startled, we all turned to him. What came out of his mouth next stunned me. I'd never heard a more comforting explanation.
He said, "People are born so that they can learn how to live a good
life -- like loving everybody all the time and being nice, right?" The
four-year-old continued, "Well, dogs already know how to do that, so
they don't have to stay as long."