Receiving a negative interest rate from a banking institution that is holding your money, seems like an oxymoron, as most people correctly associate bank deposits with earning a positive return on their money as well as being a prudent thing to do, but these are not normal times and the era of parking money in banks, by consumers, or by other banks or other financial institutions, and thereby making easy money by virtue of that money being loaned out at a high enough interest rate so as to afford the depositor a nice rate of return have ended.
While there isn't a lot of difference, unless one gets to extremely large numbers, between a small nominal positive interest rate for a depositor of money, as compared to zero interest, or even compared to a minute negative interest rate, just the fact that a deposit of $1,000,000 instead of being slightly positive after a term of one year, or the exact same amount as if the money has been stuffed inside a mattress for a year, but instead to see that the principal has been reduced to $999,999, is both unfathomable, and erringly strange.
Because we live in an era to which inflation is quiescent and in some economies and countries, deflation has become or is now the norm, so that if prices are indeed declining, it makes sense that the value of money, real cash or its substitutes, should also deflate, because in the end, because products have been reduced in price and/or are providing more bang for the buck, than even with a negative interest rate, the overall value of the money held as a liquid asset has actually gone up in value relative to the fact that the basket of products that it can buy has also increased in quantity and/or quality over the same period of time.
The reason that negative interest rates are in play comes down to the fundamental fact that in a deflationary cycle or the anticipation of such, most banking institutions make it public policy to try to get ahead of the curve, because when the public believes that pricing of products will get cheaper over time, than they will have a distinct tendency to spend less money now so as to be able to buy more later and if done in mass, this leads inevitably to a downward spiral of an economy slowing down or in fact, turning negative, which means higher unemployment, less income, less revenue, stock market collapse, and the increase of monetary defaults.
The whole point of negative interest rates is to provide an incentive for banks and banking institutions to lend money so as to maintain economic vibrancy because money or assets that sit either unused or underutilized are large contributing factors to a slowing down, stagnation, or ultimately the decline of business activity within any country, which then lends itself to the creation of an economic depression, to which America suffered through such from 1929 through 1933 and does not want to go through such an event, ever again.
The fact that negative interest rates exist and are in play signifies a seismic shift in financial markets, and is a clear signal, that the economy is in recognition that an economic abyss, is more than a remote possibility. Whether negative interest rates or the threat thereof, increases bank loans which therefore increases business activity and thereby stokes the economy actually works is questionable, but that is how the die has been cast, by the smartest bankers in the world.