Why are negative long-term interest rates a problem?

Negative long-term interest rates are shocking, but we have to understand that the only problem with negative interest rates is the existence of financial assets (banknotes, term bank deposits) that yield zero. If these financial assets did not exist, interest rates could be negative without any difficulty. The risk is then a massive switch of savings to banknotes and sight deposits, which makes it much more difficult to finance the economy, and which can be seen in almost all countries where the long-term interest rate is negative.