Take all your life savings into a savings account? Well, you could lose it all if the FDIC and your bank collapse.
Take it all into cash under your basement? You are gambling that you won't have a house fire, that you won't be robbed, etc.
Keeping US dollars at all is gambling that the US dollar retains value - there are plenty of examples of currencies completely collapsing.
i was very much infatuated by the idea of total reliability on a global scale and couldn't wait to talk about the CAP theorem with anyone who would listen. Read much of the research. I still love to flip through Designing Data-Intensive Applications by Martin Kleppmann occasionally.
As I was learning about said company's server racks there was a component that I asked an engineer on my team about – "Isn't that a single point of failure?"
He looked at me, exhausted and stressed out, and just said "Take it far enough, the Earth is a single point of failure."
I got the point.