When you're married, and you own a home (or make a mortgage payment to the bank that owns your home), and then you cross into your 30s, you will get asked how many kids and pets you have... and if you're me, you have neither.
But I grew up with dogs, both hunting dogs and family dogs, and I do love them. I just also happen to work 40 hours a week or more outside the house, plus commuting, gym, and grocery shopping time, so it has felt, for a long time, that having a dog would be unfair to the pup. But I think off and on about getting a dog, and funnily enough, the last 4 or 5 people I have floated this idea to have had the exact same reaction:
"Oh, dogs are great. They are. But if you haven't had one, or had one recently, you might have forgotten that they just can break your heart. They don't live long enough for us humans, and it can be so, so tough to lose your dog. It's just something to think about, something to not forget about."