For a year afterward, Pronovost and his colleagues monitored what happened. The results were so dramatic that they weren't sure whether to believe them: the ten-day line-infection rate went from 11 percent to zero. So they followed patients for fifteen more months. Only two line infections occurred during the entire period. The calculated that, in this one hospital, the checklist had prevented forty-three infections and eight deaths, and saved two million dollars in costs.

The executives weren't used to venturing into patient territory, and didn't feel they belonged there. In some places, they encountered hostility, but their involvement proved crucial. In the first month, the executives discovered that chlorhexidine soap, shown to reduce line infections, was available in less than a third of the ICUs. This was a problem only an executive could solve. Within weeks, every ICU had a supply of the soap. Teams also complained to the hospital officials that, although the checklist required patients be fully covered with a sterile drape when lines were being put in, full-size drapes were often unavailable. So the officials made sure that drapes were stocked. Then they persuaded Arrow International, one of the largest manufacturers of central lines, to produce a new kit that had both the drape and chlorhexidine in it.

Under conditions of true complexity - where the knowledge required exceeds that of any individual - efforts to dictate every step from the center will fail. People need room to act and adapt. Yet they cannot succeed as isolated individuals either. Instead, they require a contradictory mix of freedom and expectation. This requires balancing a number of virtues: freedom and discipline, craft and protocol, specialized ability and group collaboration. For checklists to help achieve that balance, they have to take two almost opposing forms.

There are good checklists and bad. Bad checklists are vague and imprecise. They are too long; they are hard to use; they are impractical. They are made by desk jockeys with no awareness of the situations in which they are to be deployed. They treat the people using the tools as dumb and try to spell out every single step. They turn people's brains off rather than turn them on.

Good checklists, on the other hand, are precise. They are efficient, to the point, and easy to use even in the most difficult situations. They do not try to spell out everything. They provide reminders of only the most critical and important steps - the ones that even highly skilled professionals could miss. Good checklists are, above all, practical.

Boorman was adamant about one further point: no matter how careful we might be, no matter how much thought we might put in, a checklist has to be tested in the real world. First drafts always fall apart, he said, and one needs to study how, make changes, and keep testing until the checklist works consistently.

It is common to misconceive how checklists function in complex lines of work. They are not comprehensive how-to guides, whether for building a skyscraper or getting a plane out of trouble. They are quick and simple tools aimed to buttress the skills of expert professionals.

We don't like checklists. They can be painstaking. They're not much fun. But I don't think the issue here is mere laziness. There's something deeper, more visceral going on when people walk away from not only saving lives but making money. It somehow feels beneath us to use a checklist, an embarrassment. It runs counter to deeply held beliefs about how the truly great among us - those we aspire to be - handle situations of high stakes and complexity. The truly great are daring. They improvise. They do not have protocols and checklists.

Maybe our idea of heroism needs updating.