  The term "cyber resilience by design" is growing in popularity. Here, by
cyber resilience we refer to the ability of the system to resist, minimize and
mitigate a degradation caused by a successful cyber-attack on a system or
network of computing and communicating devices. Some use the term "by design"
when arguing that systems must be designed and implemented in a provable
mission assurance fashion, with the system's intrinsic properties ensuring that
a cyber-adversary is unable to cause a meaningful degradation. Others recommend
that a system should include a built-in autonomous intelligent agent
responsible for thinking and acting towards continuous observation, detection,
minimization and remediation of a cyber degradation. In all cases, the
qualifier "by design" indicates that the source of resilience is somehow
inherent in the structure and operation of the system. But what, then, is the
other resilience, not by design? Clearly, there has to be another type of
resilience, otherwise what's the purpose of the qualifier "by design"? Indeed,
while mentioned less frequently, there exists an alternative form of resilience
called "resilience by intervention." In this article we explore differences and
mutual reliance of resilience by design and resilience by intervention.
