Tolstoy begins Anna Karenina with this observation: "Happy families are all alike; every unhappy family is unhappy in its own way." The retrospective observational study by Cheng et al. 1 in the current issue of this journal looking at the factors associated with failure to meet emergency department length of stay targets confirms again 2-5 that perhaps the opposite is true of patient flow in emergency departments (EDs): "Unhappy EDs are all alike, but every happy ED is happy in its own way." That is to say, the most common and most significant factor in what is known as overcrowding (a word on semantics in a second) is, by far, the boarding of admitted patients in the ED.In Cheng's study, 1 the odds ratio of missing ED length of stay targets for admission to the intensive care unit (ICU) was a whopping 364 (upper 95% confidence interval [CI] 3071) if the bed request duration was greater than 6 hours, and 217 (upper CI 1541) if there was "access block" in the ICU. During this time, the average hospital occupancy was 97.6% (so that almost half the time it was over 100%; and if this hospital is like others, the average occupancy of general/community medicine beds, often the destination of the majority of ED admits, may be higher than that). We know from a recent paper from Quebec 6 that increases in hospital bed occupancy are associated with an increase in 30-day adverse outcomes even after adjustment for patient and ED characteristics. Commenting on that paper, an editorial entitled "Just Another Crowding Paper" 7 laments that the finding of a 10% increase in ED bed occupancy ratio being associated with a 3% increase in death might be seen as old news. Yet, if this mortality rate was discovered to be due to an unrecognized complication of a new drug, or a new infectious disease outbreak, it would be front-page news.Cheng et al. 1 clearly described by observation what we already known with mathematical certainty given the nonlinear nature of queues: 8 if random variation in demand cannot be smoothed to any significant degree (i.e., in EDs), and capacity is fixed, and the ability to tolerate wait times is limited (another paper out of Ontario 9 showed that wait times correlate with mortality in a dose-response relationship that suggests causation), then high occupancy rates in the hospital (i.e., greater than 85% 8,10 ), leads to the ED being used as a holding area for admissions, displacing incoming ED patients into hallways and waiting rooms, which equals missed ED length of stay targets, unhappy EDs, and, most alarmingly, poor patient outcomes. We are all alike in that way.That is not to say that ED leaders and front-line staff can throw up their hands, point fingers, and blame all dysfunction on "the system." Happy EDs (in happy hospitals) have problem-solved and adapted to the myriad dynamic and interdependent factors that contribute to ED overcrowding. Like seeds that evolve to become drought-tolerant over time when there is a lack of water, EDs have evolved over time to be more efficient at rationalizing th...