[dhosek]

You’d be surprised at the numbers of people living middle-class lifestyles with negative net worth. Credit card debt, car loans (with a too-small down payment, a car purchase can easily cause one’s net worth to decline the second you take delivery on the car), underwater mortgages, not to mention student loans.

[account42]

A car purchase should mean the car counts towards your new net worth. So if it makes your net worth negative you either had almost none to begin with or paid much more for the car than it is worth.