Tacit knowledge is being able to do things without being able to explain how. We can’t learn tacit knowledge from a textbook.2 We know more than we can tell.3

Tacit knowledge7 plays a prominent part in our ability to cope with complex conditions.8,9 Every day we entrust our lives to our tacit knowledge, and not only for making left turns. We rely on it to carry out rules—to know which rules to use, to modify them as needed, and to recognize when to break them. We rely on tacit knowledge to interpret

People sometimes make up procedural guides to capture what they think experts are doing. That’s a noble intent, but procedural guides really can’t explain the tacit knowledge that people acquire over decades of experience.

Here is another way to teach procedures: Set up scenarios for various kinds of challenges and let the new workers go through the scenarios. If the procedures make sense, then workers should get to see what happens when they depart from the optimal procedures. When procedures are taught in a scenario format, people can appreciate why the procedures

For stable and well-structured tasks we should be able to construct comprehensive procedure guides. Even for complex tasks we might try to identify the procedures because that is one road to progress. But we also have to discover the kinds of expertise that come into play for difficult jobs.

In complex situations, people will need judgment skills to follow procedures effectively and to go beyond them when necessary.

Research supports this idea of eroding expertise. A number of studies have shown that procedures help people handle typical tasks, but people do best in novel situations when they understand the system they need to control.11 People taught to understand the system develop richer mental models than people taught to follow procedures.12

Procedures can lull people into a passive mindset of just following the steps and not really thinking about what they are doing.

Inevitably, the procedures lagged behind the actual way people did their work. Up-to-date procedures had to be interpreted and carried out by workers using their judgment and experience, and obsolete procedures created even more headaches. But there is a bigger problem than the fact that procedures are rarely sufficient and often out of date. In