Why is 10% the necessary upper bound for a negative interest rate?
Assuming your home is safe, would you keep your money in a bank that only gave 96% of it back? (-4% interest rate)

What if your home has mice which eat exactly 10% of your money? Would you then keep your money in the bank that only returns 96%?

And finally, what if every bill has a 10% chance of being eaten? This means that in expected value you lose 10% of your money.

In the above situations, what would be the lowest interest rate you would accept from the bank?