system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a second mortgage and why is it bad?
gpt
You buy a home for $100 dollars, and borrow all $100 from the bank.  After some time you only owe the bank $80, and the home is worth $120.  Now you can take another loan on the $40 on the part of the house that you own.

The loans can be bad if you get in a position that you can't pay on both the $100 loan and the $40 loan at the same time.