JP Morgan estimates that over $5.5t (yes, trillion) of investor funds are currently in negative yielding government bonds. To put that into plain interest, if you purchased $10,000 (Euros to be correct) worth of German 5 year bonds currently at -0.308%, after 5 years, your $10,000 would be worth $9,846.94.
To clarify, this doesn’t mean that the quarterly interest payments are negative, it means that the amount an investor is prepared to pay for the bonds is so expensive, that when it matures; combining the capital being repaid (the face value) and any income generated works out that the ‘total return’ or ‘yield‘ is negative.
If, like most people, you are asking why someone would invest into a bond which returns negative yield, this article discusses a few ideas, mostly that it is about having liquidity (meaning they can access their funds quickly if needed). However there are a number of reasons behind this and trying to pin point exactly why is a waste of energy, it just goes to show that looking to the past to predict the future will be a fruitless exercise.