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.
This is the reason I don’t use a password manager. I don’t trust all my security to a single app. The idea that if one app is compromised all my information is compromised.
Single point of failure is something that you should keep in mind for any system you are building, personal or professional. Don’t put all your eggs in one basket and let one issue cause more problems than it should.