system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why would anyone buy a bond with a negative yield?
gpt
Lots of reasons:

1. you're buying \_your own\_ bond.  Most bonds require a liquidity level in the issuer to match obligation out there, and buy buying back they can decrease the liquidity level required. 
2. they may be effectively trading \_currency\_ - e.g. they currency it's issue in is going to change in value so the very small loss in bond yield is made up for in currency change (relative to some other currency).  
3. They may believe they are entering a period of probably loss in portfolio value but think the most secure place for their money is in a bond that has a very predictable, but reliable loss.  E.G. if you believe a market is going to tank by 15%, then finding the strategy that loses 0.5% is \_really, really good\_.