Being a dog owner involves a certain amount of self-delusion. Rationally, you know the lifespan of a dog is short. Unless you get your dog when you’re 75 or you get into some horrific accident, you’re going to outlive your dog. This animal that loves you unconditionally, depends on you for everything, would likely give its life for you, will die before you do.
So one of the most important rules of dog ownership is you never, ever, ever let yourself think about it.
Until the day comes when you have to think about it.