For me, I have made mistakes with my dogs over the years, and one in particular I kept alive for too long - bless her, she was almost 20yrs old, completely blind, completely deaf,
and had bad arthritis too ... her quality
of life was very poor, but it still took me a year to decide to put her out of what misery she was in. I feel it was entirely selfish on my part, but it was such a hard thing to do.