Yeah, many people lack the forethought required when adopting/buying.
I have to be honest, I am somewhat guilty of this. I want a GSD so bad I don't think about the fact that I am going to college in August. However, when it all comes down to the decision, I know I can't have a pet for the next 5 years, at least. It drives me crazy, but it means that the dog and I end up with will have a stable home.