For those with real estate knowledge, if you have say a $500,000 mortgage but sell your house for $400,000, do you have to write the bank a check for $100,000 on day of closing? What if you don't have that much money?

Million of americans owe more on their mortgage than their house is worth. You'll be in default of your mortgage if you can't pay it off in the event of a sale and your credit will be ruined, don't plan on buying another home.. you'll be a renter for many years to come.