So, forgive the ingenuity, what prevents me from taking that 1000 loan, park it in my bank account, and repay the 990 due in a year (earning 10 in the process)?
The other side of this rate is that the (central) bank will also charge you for holding that money parked, instead of paying you interest. That plus inflation is (supposedly) offsetting your gain, so you might as well loan out that cash to make real money - which is what the rate-setter wants.
This said, the technical answer to your question is something between "not much" and "nothing at all". Some central banks attach strings to what you can do with that borrowed money, but not all. This is why the effect of negative rates is still debated.
Your bank is going to start charging you interest as well. They might have a teaser rate that's positive up to a certain balance, but there's limits to the arbitrage here.
1. Inflation: you will have 10 at the value of the currency in 2022, not 2021
2. Negative savings rates:
> There are fears that negative lending rates, which are expected to lower borrowing costs for households and businesses, would force high street banks and building societies to offer negative savings rates.
If you put it in your bank account you will lose some of it. The idea is that the bank is paying you to hold the money because otherwise it would have to pay the central bank more than that to hold (some of) it - or at least, that's how I understand it.