Emergency departments (EDs) often seem to shift from calm to crisis in an instant. Why? This article explores ED crowding through the lens of complexity science and self-organised criticality, explaining how minor changes—like a few extra patients—can trigger disproportionate chaos. Using the sandpile analogy and concepts like power law distributions, we reveal why traditional linear models and static targets often fail to manage ED flow effectively. Instead, we offer a data-driven, systems-based approach: identifying tipping points, recognising early warning signs, and implementing proactive, anticipatory interventions. From real-time dashboards to weekly cycle planning and distributed decision-making, this article offers a practical guide for building resilience in emergency care. Learn how your ED can thrive in complexity, not just survive it.