As a prospective puppy buyer/dog owner, you must be aware of the traits, both good and bad, of the breed you are considering.
Many pet owners own the breed they do because of an impulse buy.
Sometimes this works out fine and other times dog owners find out, too late, that this is not such a wonderful breed (for them) after all.
Sadly, it's the innocent dog that suffers when it gets placed in a new home, returned to the breeder or, worst of all, taken to the pound! Each breed was developed with a definite purpose in mind.
Each breed (or most anyway) have breed specific health and or temperament problems of which you should be aware.
Some breeds have coats that need hours of grooming to keep the dog in good shape.
Some breeds shed more than others.
Some breeds are very active and hyper while others are quiet and sedentary.
Because different breeds have different characteristics, it's a good idea to first define exactly what traits you want in a dog.
Do you want a large dog, medium or small? What is the main purpose of having the dog, other than companionship? Do you want the dog to hunt with you? Do you want a dog that is a good guard dog? How about children? If you have them, you want to be assured that the breed you choose is going to get along with the kids.
And if you do have children, what age are they? A dog breed that tends to be very hyperactive and aggressive would not be a good choice with very small children as the dog will likely do damage if it jumps on the kid and play bites.
However kids in the 10 years and up range would probably thoroughly enjoy an active outgoing playmate.
What about grooming? How much time are you willing to spend on this chore? What about shedding? Some dogs don't shed at all and others shed almost constantly.
How much noise are you willing to put up with? What about trainability? Some breeds are notoriously difficult to housebreak and/or train while others practically discipline themselves.
If your interest is obedience, seek out those breeds that excel in the field.
If you're a hunter and have visions of fall days in the duck blind with your trusty dog, you wouldn't go out and buy a Chinese Crested.
If you hope to own a dog that will be around for 15 to 16 years, don't purchase a large breed.