I was recently reading some articles about why people say they are giving their dog up to a shelter as well as a study of owner satisfaction a year after adopting a dog from a shelter.
Those who gave up their dogs were most likely to say they were giving up a dog for behavior reasons.
Those who adopted a dog from a shelter and lived with it a year were happiest with dogs who met their expectations.
To me, both of these points have something to do with the overlapping areas of 1) training a dog; 2) matching one's self up with a dog who can give what one expects.
For example, let's suppose that a person has a young family, with toddlers, and wants a dog that will fit in with the kids, and quickly pick up the family routine, but not require a lot of extra work. And then this person observers that there is a very young, energetic English Bull Terrier for adoption and this person runs out and adopts the dog (I know of a situation where only a vigilant shelter manager stopped this from happening.)
This is a recipe for a dissatisfied person and a dog that would probably end up being rehomed with one of those annoying ads I am constantly seeing, which says something like, "Need to find loving home that will love our dog as much as we do, we no longer have time for her...."
Young Bull Terriers (like many young animals) are very energetic; running dogs are prone to knocking toddlers over in joyful enthusiasm. They don't 'just pick up' the rules and expectations of a family, and they require extra work in the form of exercise and attention, which a young family may not have to spare given the demands of the toddlers themselves. This isn't to say that a mature member of the breed, who has settled and been trained couldn't be added to the family; breed characteristics, level of training a dog already has, and a family's current situation should all play a role in choosing a canine companion that will fit into a family.
I maintain that if people put as much time and thought into choosing a canine companion as they do into selecting a computer they will buy, or commit to a dog and training for at least as long as they would have to commit to a phone company contract, fewer dogs would be disappointments or would require rehoming due to the 'time commitments' of people.
For those of us who have anything to do with dog adoption this is also a reminder of the importance of thorough screening of potential owners. It really is better for a dog to stay in foster care/shelter a little longer, then to send them out the door with a family that is a poor fit.