The number of people in the organization who have unique critical expertise should be kept low
The number of people in the organization who have unique critical domain expertise should be kept low. Minimize the probability that the loss of any given team member would mean the loss of critical expertise. Build a culture of shared knowledge that increases the breadth of knowledge over time.
Ideally, all projects could survive the loss of any one member. The rather gruesome origin of the name arises from asking the question “If this person were hit by a truck, how would the project be hit?” When looking at other patterns, it should be noted whether they tend to increase the truck number (e.g. OwnerPerDeliverable) or whether they act to reduce it (e.g. CollectiveOwnership, DevelopingInPairs). Ultimately there will be some trade off between the risk of loss of critical expertise and the cost of duplicating that expertise. Modern approaches tend to decrease the cost and increase the benefit of skills transfer, so the balance is shifting toward reducing the risk.