[Someone]

”The interest rates go below 0 because investors don't trust banks with their money.”

If investors didn’t trust banks, they would demand high interest rates when borrowing banks their money, just as they demand higher interest from those who want to make smaller down-payments on houses, or on credit card debts.

Looking at https://www.investing.com/rates-bonds/european-government-bo..., many European countries (even Spain and, short-term, Italy) can borrow money from the market at negative interest rates.

That must mean those borrowing them money must be confident they will get that money back (not that surprising, given that the ECB keeps printing money)