Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

Why is being “upside down” on a mortgage so bad?
Sample Numbers: Owe $100k on house.  House (after 'crash') valued at: $50K.  Reason for consternation: What rational person pays $100k for property that is only worth half that amount? True Story: My neighbor paid almost $250K (a quarter-of-a-million dollars - think about that..) for a house that when he walked (ran!) away from it was sold by the bank for $88K.  Unless he declares bankruptcy (and forgoes all his other assets, including retirement savings) he still owes the bank the difference. And even with bankruptcy, he may still owe the bank - this should cause anyone to be a bit concerned about being up-side down in a mortgage loan.