This research note introduces the Mallinckrodt Instability Principle, a conceptual framework for analyzing systemic fragility in complex adaptive systems. The principle proposes that systemic instability often emerges not primarily from randomness or chaos, but from the accumulation of structural compression under conditions of stress, which gradually reduces a system’s adaptive capacity. Across many domains of complexity science, researchers have observed that systems can become increasingly brittle as internal structures designed to maintain stability accumulate over time. While such structures initially enhance coordination and efficiency, they may also reduce flexibility, diversity of responses, and the ability to reorganize in the presence of external shocks. When structural constraints grow faster than a system’s adaptive capacity, the system may lose its ability to respond effectively to environmental change. The Mallinckrodt Instability Principle summarizes this observation in a minimal conceptual form: A system becomes unstable when structural compression under stress exceeds its adaptive capacity. To operationalize this intuition, the paper introduces the Compression–Resonance–Tension Index (CRTI) as a simple diagnostic ratio: CRTI = (C × S) / A Where: C — Structural Compression Density of constraints, institutional rigidity, network coupling, or rule accumulation within a system. S — Systemic Stress External perturbations, shocks, volatility, or environmental pressures acting upon the system. A — Adaptive Capacity The ability of the system to reorganize, learn, absorb disturbances, and generate alternative responses. The CRTI is proposed as a heuristic diagnostic indicator that may help identify conditions in which complex systems approach instability thresholds. The aim of this work is not to present a complete theory of systemic collapse, but rather to outline a minimal analytical framework that connects insights from several existing research traditions, including resilience theory, cybernetics, and nonlinear dynamics. The framework is intended to stimulate further research into measurable proxies for structural compression, systemic stress, and adaptive capacity across different domains. Potential applications include: organizational systems and governance structures financial and economic networks technological infrastructures and digital ecosystems ecological and environmental systems Future work will focus on operationalization, simulation experiments, and empirical case studies that test whether the proposed index can function as an early diagnostic signal of systemic fragility. This publication therefore represents an initial conceptual step toward a diagnostic approach to systemic instability, rather than a finalized theoretical model. Keywords complex systems complex adaptive systems system instability structural compression adaptive capacity CRTI index cybernetics resilience theory nonlinear dynamics system diagnostics organizational resilience systemic risk complexity science early warning signals systems theory complexity science systemic risk early warning signals network fragility