Earlier quoted context omitted.
This is an example of how to write a good article, I think the first sentence answers your question: "Germany sold 30-year debt at a negative yield for the first time, as investors desperate for safe assets bet that further falls in yields will boost the value of the bonds in the future." The investors buying these bonds are simply betting that these bonds will increase in value (which will supposedly happen if centr…
The implication then is that we're in a bond bubble. When you're buying something that you know has negative fundamental returns on the assumption that someone will buy it from you at a higher price, that's the definition of a bubble. And like many bubbles, it's entirely possible they'll be right in the short term, but it's basically guaranteed that they'll be wrong in the long term. You know exactly what a bond will…
When people were selling houses in Detroit at the bottom of the housing crisis for $1000, the people buying them were expecting the value to rise in the future.
It's almost like profiting off of fear not greed.