I have a good example. When our dog, "Rose" (Husky/GS x BC cross, 2007-2016 RIP) got sick from (my Vet thinks) bone cancer, we only saw her jaw fuse shut. She was breathing through a straw and GS Breeders (and Vets) are so desensitized to these abnormal genetic diseases that they are not as shocked as I was to realize that this could even HAPPEN. We had her on Prednizone, big doses, and she was really miserable. One night we were leaving to go out to dinner and DH said to give her a Vicodin, His dose. I thought it might kill her or make her feel better. She had been in so much pain that we saw the happy dog we had had one year earlier when we came home. THAT told me that is wasn't right to keep her on bandaid medicine that had only partially fixed the atrophy in her jaw muscles. I had my Vet come out and she was put down in my arms about a week later.
We also put down on 27yo QH bc he had 5 ailments, including arthritis, and developed a 6th one. We had had a horse that developed Cushings (aNOTHER ailment I wasn't familiar with) and he went down and it took forever for him to pass. MY QH had been my babysitter loyal companion from the time we retrained him as a 7yo, and I did NOT want to watch him suffer.
It sounds grim, but I have our GS/Collie cross, "Xena" (1998-2008, RIP) buried under four 16 x 16 cement pavers, Rose is next to her buried under the same, and I plan to buy 4 more of the same pavers for my dog, "Pyg", who will be 10yo in November, when her time comes. Fortunately, she still runs and plays and does her "Pyg jobs" around the farm.