Guideline: Build to fail securelyPart of: Development Security Guidelines
Overview: Building a set of Guidelines for Security and Privacy
This guideline is not about fail safe. Failing safe is about that functionality resumes when a certain control fails to operate. Failing secure is the opposite of that. In example can illustrate that better.
A firewall is a security control that can be, for instance, placed between the Internet and your internal network. When this firewall fails to operate, a couple of things can happen. Either the entire internal network can access the Internet and vice versa (fail safe) or access to the Internet is entirely shut down (fail secure).
More information from OWASP about a Fail securely.