You own shares of the fund. Imagine it's like a company that makes a bad decision and loses all of its money. Maybe it ends up with debts greater than its asset

You own shares of the fund. Imagine it's like a company that makes a bad decision and loses all of its money. Maybe it ends up with debts greater than its assets. Either way, you as an investor lost the entire value of your shares which are now worthless, so $0 is as low as your investment can go. You're not responsible for paying any of the company's debts if they exist.