This research note introduces the concept of Structural Drift, a phase of gradual directional misalignment that precedes observable instability in complex systems. While existing early warning research has focused on Critical Slowing Down (CSD) as an indicator of approaching tipping points, Structural Drift describes an earlier phase in which system directionality deteriorates while observable state variables remain apparently stable. The paper proposes a three-stage collapse dynamic: Structural Drift → Critical Slowing Down → Collapse. This framework highlights the importance of directional variables in system analysis and provides a conceptual explanation for why many systemic collapses appear sudden despite long underlying deterioration. The note situates Structural Drift within the broader literature on critical transitions in complex systems and early warning signals.