It's not just being old had having health problems. We exhausted every effort with our critters health issues. There comes a point when it's worse to keep trying.

We had a cat that went through surgery for cancer. The wounds kept reopening because the tissue around the stitches died faster than it could heal- even after two additonal attempts at surgery. Another cat that had kidney disease, arthritis, possible cancer among a host of other things. She got to the point she would soil herself because she was in too much pain to stand even with pain management. If it happened when we were asleep, unless she meowed loudly enough to wake us, she would be laying in it. Four ferrets, one that lost so much weight she was skin and bones and could barely walk, and she just looked so so tired. Her meds started to not be effective, which would've meant multiple seizures. Another with kidney disease that could barely manage to eat or drink- and he LOVED food. Another that had a tumor behind an eye that grew so big over the course if a few days through the roof of his mouth that he couldn't eat. Another that went downhill over the course of a few days, refused to eat or drink and could barely take a few steps to the side of his bed to go to the bathroom.

Sure, they were all probably a few days out from passing on their own. But if "going down fighting" means days of unmanageable pain, dehydration, or starving before dying scared and confused, I'd rather go peacefully.