Here's a simple example:
John Doe has a $250,000 home. Financial troubles occur and John can't pay the taxes, so he ends up owing $10,000 to the government. Right after, the government shows up and throws him out of his home... putting the home into foreclosure.
A few weeks later, the home is sold for $200,000.
What happens next is…
the government takes the $10,000 John owes... but what happens to the extra $190,000?
Who gets the $190,000 that's left?