John takes to Medium to explain Dark Debt with excerpts from the Stella report.
The challenge of dark debt is a difficult one. Because it exists mainly in interactions between pieces of the complex system, it cannot be appreciated by examination of those pieces. After anomalies have revealed the relationships they appear obvious but the appearance is mainly hindsight bias (Woods & Cook, 1999). The existence of dark debt poses a substantial challenge to system owners.
Unlike technical debt, which can be detected and, in principle at least, corrected by refactoring, dark debt surfaces through anomalies. Spectacular failures like those listed above do not arise from technical debt. Critics of the notion of dark debt will argue that it is preventable by design, code review, thorough testing, etc. But these and many other preventative methods have already been used to create those systems where dark debt has created outages.