Your rental property went down in value so much that it was worth less than your $500,000 mortgage, so you walked away from the property. Let the bank enjoy it!
You pat yourself on the back for your clever move until the following January. January is 1099 time and you get a 1099-C from the bank stating you have $500,000 of cancellation of debt (COD) income
Your cronies at the club tell you that you have to pay US and NJ income tax on the $500,000 at ordinary income tax rates, not the favorable capital gains rates. You calculate that your brilliant move will cost you $200,000.