The sheepdog story originated in a lecture at the USNA by William J. Bennett in 1997. Since then, retired LtCol. Dave Grossman, author of
On Killing, has capitalized on Bennett's lecture, and makes a tidy income from frequent speaker's fees, quoting Bennett's lecture while promoting his own books.
Here is the Sheepdog story:
http://hobbes.ncsa.uiuc.edu/onsheepwolvesandsheepdogs.html
While I have some issues with a few of the aspects of the "sheepdog" anecdote, and a few with Grossman's "On Killing", both are well worth reading, instructive, and give a good perspective on the subject.
However, while I'm no psychologist, I do have some personal opinions upon why some people remain spectators when they should not. And why others act.
I have known a few friends – strong-willed, aggressive, and out-in-front type guys - who have said what they would do in certain hypothetical situations. And I certainly believed them. Then later, when they actually did encounter the same situations they had hypothesized, they found that they didn't act anywhere near as they had thought they would. Why is that?
Life and death situations do not normally occur in our lives. They are extremely rare. But when they do, it is primarily our expectations, preparation, and most importantly,
our training that determines our actions.
Walking along a busy street in a safe neighborhood, your squadron mate is suddenly stabbed by a passerby. Unless you have trained, or have expected such a threat, this out-of-the-blue action leaves you suddenly in shock and disbelief – for just a moment, you are stunned. You are inactive. (It's the same theory behind those "flash and stun grenades" effective against hardened militants)
If the attack persists, you will try to respond. But your response will be slow, and not at 100%, because you still are surprised, and cannot quite comprehend nor assimilate what is really taking place. Your disbelief slows and drags upon your response. And if the victim is not your "squadron mate", but a total stranger, your reaction if far more slowed as you try to figure out what really is happening, who are the good guys or the bad guys, why is this happening, what are the risks, what can I do, this can't really be happening, can it? Why is this happening? Is this real? Etc., and etc.
Some very few people – and far less than the many who would like to think they would – will react immediately and effectively. But they are the people who have either been trained well for the situation, or have practiced it repeatedly in their minds, or they are the very select few who are hard-wired for immediate and without thinking or pause, reactive response.
While many of us would like to think we are the later personality, those people are extremely rare. (And many of them don't live long either, but they are still to be revered.)
In a life & death situation, your IQ instantly drops by 75%. (I think, more or less.) So when you are thus made very stupid, it is only instinct and training take over. That is why a Marine DI can take the most sniffling momma's boy, and with a little 'training'', and later more specific hardened training turn that weak individual, through repetitive training, to instantly react proactively – without stopping long to analyze such an "unknown" or "unexpected" threat as a stabbing of your buddy in a safe, downtown neighborhood. Through proper training, the former sniffling wimp might well perform well above that of the more 'ideal' warrior, because of his specific and intensive training to react in such a situation.
Most of us are not so trained to react.
Like many of us, I have run many threatening and various scenarios through my mind. So there, we all have a leg up. And some of us have specific training; indeed, another leg up. But like my friends before their incidents, none of us truly know how we really would respond to certain threatening situations. My military friends said their responses were far different than they had originally imagined. That is why I am reluctant to judge anyone in such situations.
[As far as the 'perps' beating up the old WWII Vet, I hope and I'm sure they will be caught and sentenced. And for this specific crime, they will certainly and rightly so, suffer in prision. The 'cons' don't like that crime and will take out their own retribution.]