FM8 — Schema/Contract Violation: The most expensive technical debt creates implicit contracts. Shared database schemas are implicit contracts between every application that reads them. When the schema must change to repay the debt, every application that reads the schema is a change site. The cost of repayment scales with the number of consumers of the implicit contract.
FM11 — Observability Blindness: Debt in the observability layer is particularly dangerous. Systems with no structured logging, no metrics, and no tracing are opaque. Incidents take longer to diagnose. This makes the MTTR metric high, which increases the business cost of the next incident, but does not by itself motivate fixing the debt — because without observability, the true cost of incidents is invisible.