Single Point of Failure
It’s a pretty common idea in a lot of fields (business, security, software development, etc..), try to avoid a single point of failure. Don’t create any system that can be completely taken down by one problem.
Would you write in a notebook if it came with a warning that there is no guarantee that the ink will stay on the page or the pages won’t spontaneously combust? Or that there is no way to know if other people are reading your notes? That you don’t actually own the information you write down?