OK. We can take it as a near-given that in any given robbery of a store, the direct impact of the loss of money (which will be probably only a few thousand dollars at most) is far outweighed by the costs incurred if somebody gets shot (everything from lawsuits to the downtime and expense of having somebody come in to clean the blood and brains off everything that got splattered). So the preferred outcome is one where nobody gets shot at.https://www.ncjrs.gov/App/publications/Abstract.aspx?id=142068
"Results revealed that self-protection of any kind apparently reduces the probability of the robbery being completed. Armed resistance is more effective than unarmed resistance; resistance with a gun, although relatively rare, is the most effective victim response of all. Resistance with a gun also appears to reduce the likelihood of the victim being injured. However, two types of resistance appeared to increase the risk of victim injury: (1) unarmed physical force against the robber and (2) trying to get help, attract attention, or scare the robber away. The robber's possession of a gun also appeared to inhibit victim resistance, which can sometimes provoke a robber to attack; robber gun possession thereby reduces the probability of victim injury. However, even controlling for victim resistance, robber gun possession is associated with a lower rate of injury to the victims. Tables and 45 references (Author summary modified)"
Note point 2: "trying to get help, attract attention, or scare the robber away". In other words, even if pulling out your own gun is a good way to defuse a robbery attempt on your person, what McClean did was one of the cases where you end up increasing
the chances you'll have to pay to get the blood cleaned off everything...