But there was probably something else, something more subtle and cultural, at play. Today, many healthcare organizations study the Toyota Production System, which is widely admired as a model for safe and defect-free manufacturing. One element of the TPS is known as “Stop the Line.” On Toyota’s busy assembly line, it is every frontline worker’s right — responsibility, really — to stop the line if he thinks something may be amiss. The assembly line worker does this by pulling a red rope that runs alongside the entire line.

When a Toyota worker pulls the cord for a missing bolt or a misaligned part, a senior manager scrambles to determine what might be wrong and how to fix it. Whether on the floor of an automobile manufacturing plant or a pediatrics ward, the central question in safety is whether a worker will “stop the line” — not just when she’s sure something is wrong but, more important, when she’s not sure it’s right.

Safe organizations actively nurture a culture in which the answer to that second question is always yes — even for junior employees who are working in unfamiliar surroundings and unsure of their own skills. Seen in this light, Levitt’s decision to talk herself out of her Spidey sense about the Septra dose represents one nurse’s failure in only the narrowest of ways. More disturbing, it points to a failure of organizational culture.