negative yielding bonds means it will yield negative return if you hold it to maturity . The point to be noted is will you hold it to maturity ? Most of such bonds are traded and plus don't forget yields are present value estimate of possible interest rate path. Will the economy continue to stay in recession for 20 years and deflation exists and you will hold the bond to maturity then you will make negative returns . That's too many things going the same or " pessimistic " way