It's human nature, I think. We don't consider the mortality of those we love. We somehow just expect them to all outlive us. Even when our family members are older than we, we are still capable of living our daily lives without the expectation of losing them.
It's different with our animal families though. There is finiteness to our relationships with our beloved pets. When they come into our lives, we are fully aware that it is a temporary gift. We know we will outlive them and we know we will mourn them.
My brother and his girlfriend are morning Karma today. And so am I.