The adult elephant: We must confirm danger to ourselves before firing. This is the big one. Consider the classic and not-unusual training scenario (and real-life event, too) of a subject turning on a police officer with a glinty object in his hand, held in front of him. Officers are supposed to wait to confirm the nature of the object in the hand before making a decision to fire. But if they wait to verify that the object is a gun - instead of a badge or cell phone - we all know that it will be too late. Common sense, everyday experience, decades of demonstrations, and actual research indicate that in circumstances like the above, if we wait to confirm the threat, we will give our potential assailant a guaranteed window of time in which to harm us. In these cases, as Kelly McCann puts it so well, "confirmation of the subject's intent will come in the form of harm to us." In some training, officers who do fire at what turns out to be non-threat targets are reprimanded, remediated, or at least made to believe that they screwed up. Too often they are not told that they were placed in an impossible situation. Sometimes such "errors" are even recorded in their permanent file as a scarlet letter, waiting for the right inquisitor to come along.
On the street, when officers choose to live rather than maybe die in that split second in these kinds of situations and shoot, it can be hell to pay if the subject was unarmed. Often, their own administrations and the public abandon them. They are told by their (often exclusively range-based ) trainers that they failed, and are failures. They are fired, sued, and their lives ruined, all for being forced to make a devil's no-win decision. Not always, of course. Sometimes the officers are supported and their decision understood. And even while the vast majority of LE shootings are ruled justifiable, too often we see the situation I have just described.
Of course, the actual law (and the actual morality of decisions to shoot) is that we must reasonably believe that a suspect presents a threat of death or crippling injury to ourselves (or others.) We don't have to actually confirm without doubt the threat before firing.
What to do? We have to admit that if society is to have an effective police force, there will be unfortunate casualties, much as if we insist on having individual modes of transportation (the automobile), there will be unfortunate casualties (currently about 40,000 of them a year.) We have to admit that police officers sometimes have to make impossible decisions with incomplete data in time frames too short to provide accurate information.
We need to educate the public that lawful gun owners never, ever turn on a police officer except very slowly and in response to direct orders form them. (This is easier with state mandated, standardized education for permit holders.)
We should not teach our people that they are screw-ups when the situation is such that they can't make a proper decision no matter what they do. In training, we need to focus on tactics that mitigate the advantage that a suspect has in the kinds of scenarios described above. We need to focus on verbalization skills, such as "police officer, do not move!" (which is not always possible for real), and seeking and working from cover better (which is also not always possible.)
CAVEAT: I trust that no one will take the preceding as a plea to lower decision-making standards in training or on the street, nor to encourage a shoot first and ask questions later mentality, nor to encourage the practice of spray and pray. I just want us to recognize that sometimes officers are asked to make a decision that is literally no-win. When we present these situations is training, we should acknowledge to the officer that it is in fact a no-win situation. When officers have to make these decisions on the street, we need to support them.