Edit: this comment was written in response to the parent before it was edited to remove any trace of what was being replied to.
When the US Treasury (or WeWork) sells a bond at $100 (and it almost always does), it is based on a face interest rate (say 3%). This interest is fixed (eg. the bond will always pay $3).
If prevailing interest rates rise to 4%, then the price of that bond will drop to a price such that the interest the bond pays ($3 per $100) ends up being a 4% yield.
It also works in the opposite direction and this is how you end up with bond prices above $100. The price has to swing higher for that $3 per $100 face value to have a yield less than 3%.
As an aside, this is also why longer term bonds are riskier than shorter term bonds, you can lose significant amounts of money if interest rates shift higher over 10-15 year timeframes because the market price of the bond will have to drop to make it competitive in secondary markets.
See https://www.bloomberg.com/markets/rates-bonds/government-bon...
And the US Treasury can print money, but it's got it's own issues with a congress who occasionally has members who grandstand and threaten to default on debts. Meanwhile, Germany runs a surplus budget. I'm not saying that US Bonds aren't extremely safe, but it's hard to know if German bonds are really less safe. The market seems to consider them extremely safe. The biggest risk with German bonds for a buyer who transacts in dollars is currency fluctuation
But I agree with your sentiment with regard to the original comment you responded to (which seems to have been edited now).
It's more of a currency based risk. You're probably right that Germany is as safe of a bet (if not more) to pay back their bonds than the US is. The question is how much 100 Euro is going to be worth in 10 year.
Bonds have a face value (which you get paid at maturity) and a coupon (interest payment calculated as either a fixed percentage of face or as a spread over an underlying rate * face)[1]. Both of those components matter to investors and factor into the so-called "yield to maturity" of the debt. The bond price dropping means that the secondary market is demanding a higher yield to maturity on the debt.
The main drivers of that price are the underlying risk-free rate of interest (which compensates investors for the difference in utility between having cash now and having cash in the future and essentially arbs out between all the different risk-free or near-risk-free instruments they can invest in) and the credit spread (which compensates them for the likelihood of default and arbs out with other instruments of similar riskiness and the prices of things like CDSs).
In the 1yr T-bill example, almost all of the price discount you are quoting is about the risk-free rate of return. So say the rates were at 4% when a 10yr note was issued, we are now in the final year and rates have gone up since then, then the price of the bond would drop so that investors get a yield-to-maturity on this bond that is approximately the same as other instruments of equivalent maturity.
The WeWork example is going to be driven by the credit spread - how likely WeWork's is to default and how much investors would be likely to recover in that event. The price going down is to do with the credit spread widening and therefore investors demanding a higher interest rate to compensate.
[1]I'm simplifying a lot here given all the weird and wonderful types of bonds you can get.
"There isn't an institution in the world that could sell an IOU $100 for $100" is not true