Economists are obsessed with watching how this line wiggles over time, in their words, it says a lot about the economy and where it is headed. Believably it has always predicted an economic recession without fail. So how does this work?

The explanation is mostly straightforward. If you buy a US treasury bond, which is considered to be the safest investment there is, you get interest paid back. The longer the note, the better the interest because there is a greater risk. So for Feb 2, 2021, it looks like this.