I say with only a little shame that I am guilty of the “sin” of coveting my neighbor’s dog many times over. It’s so easy to do, and yet I advise against it because it’s unlikely that anything good will come of it. Sure, once in a while you want a dog who the neighbor can’t keep because of failing health or some other extreme situation. In other cases, the dog that is a perfect match for you just wasn’t right for the original guardian, and a change is positive for all.
These win-win situations are not the norm, though. It’s far more probable that you end up pining for a dog who can never be yours even though that dog might make you very happy. Another possibility is that the dog you long for would not, in actual fact, be a wonderful addition to your family and to your life.