Dirty, messy, smelly, expensive to keep, particularly if veterinary care is required, need walking frequently, many want lots of exercise which you have to give them however busy or ill you are, limits your freedom to go away, has to be cleared up after unless you can always walk in the countryside, sits on all the best furniture and if, cruelly, you don't allow that then it leans on it instead, making it grubby in a strip a few inches above the ground. Claw marks on the doors. Toothmarks on the chair legs and holes in the towels if you have a puppy, as well as stains on the carpets and puddles on the floor. All combine to make an excellent case for not having a new young dog, although of course a dog you've had for a long time, when you know each other's ways and it's trained, to a greater or lesser degree, to the extent you're happy with, is fine and you tend to forget the difficult bits.
But. Be without a dog? Couldn't bear it. It's worth every minute of it.
I'm depressingly sensible and I've explained already (albeit in March) how it came about that we didn't acquire a puppy in the last few years and why I'm not looking to get one now for Tilly's sake. And I know it wouldn't make sense to have a dog that needed a lot of walks before I have, and am recovered from getting, a new hip (though I reserve the right to be entirely silly and get one anyway) but simply, when it comes down to it, if a dog needs a home, I'll give it a home and love it, and when our Tilly dies, which I hope won't be any time soon, I am sure we won't be without another dog for long.
There are enough indications, after all, that generally speaking people with pets are happier and more relaxed than those without, though I can't believe that anyone would solemnly buy a cat or dog with the intention of being happy unless they actively wanted one anyway. I do know people who've bought a dog to make sure they have an incentive to get more exercise, but again you have to want one. There's no doubt that a dog gives added security, both to the owners personally and to the house where it's kept.
It's still simpler than that, however. If you're sitting alone in a room reading this, now think of doing it with a warm body on your lap or leaning against your leg. Imagine glancing down and seeing the warm brown (more likely than not) eyes looking at you with total trust and devotion. Think that, however much the exercise will do you good, you wouldn't dream of going for a walk on a rainy winter's night, but that you'll do it without hesitation for the sake of your pet, and actually you'll enjoy it and feel the better for it. Remember that, however bad you feel, whether through loneliness, depression, illness or because you've done something you regret, your dog will love you just the same, stupid loyal creature that he is. He will be on your side, no questions asked, even if you lost your temper at his naughtiness a few minutes ago.
I like cats and I have an affinity with horses, but it'll always be a dog for me.