A dog is shot by the owner. How would you feel in this situation?

Years ago, my sister and BIL had a beloved German Shepherd dog. Chance (the dog) grew old and was experiencing health issues, albeit none terminal, as far as I recall. The BIL took him for a walk on their extensive property before putting a bullet in Chance’s head.

In one sense, it seems like an act of love. On the other hand, one has to wonder about the mindset of human that would do this.