When you're confronted by a gunman, it's usually best to do what you're told.
Not any more though.
Not any more - by a long stretch.
The terrorism attacks in Paris have confirmed everything that Western security experts have long suspected.
And that can basically be boiled down into one key principle: whatever the terrorists tell you to do, you want to be doing the exact opposite.
They tell you to stand still; run like hell!
They tell you to lie on the ground; hurl your bag in their face!
They tell you to "keep calm"; become a screaming, whirling ball of frenetic energy.
And the reasoning behind this highly risky course of action is this: these terrorists want to kill you. These bastards want you dead.
They do not want to negotiate. They do not want hostages. They do not want bargaining chips.
Their sole goal is to die a martyr's death and to kill as many damn Westerners as they possibly can.
And if you do what they tell you to do, you're just making their job a whole lot easier.
If you were a terrorist gunman, who would you prefer to shoot? A nice docile bunch of people who are lying on the ground, so you can pick off the trouble-makers one by one and then take your time slaughtering all of the obedient passives on the floor?
Or would you fancy shooting at a crazy mob, everyone running, screaming, maybe some of them heading straight at you?
Whatever the terrorists tell you to do, you've got to be doing the exact opposite.
Look: I'm fully aware that it's not a great scenario and that you'll probably end up dead. Generally, with a gunman, you want to be doing just exactly what they tell you.
But if you are unlucky enough to have been caught up in an Isis shoot-out, then you must realise that your chances of survival are very, very slim.
And if you do what they tell you to do, you may have bought yourself a few extra minutes. But ultimately: if you lie down and keep quiet, then you're much more likely to end up dead.
Perhaps I ought to offer up the credentials on which this off-the-wall theory is based. I am well aware that it's the complete opposite of the pliant attitude that we're supposed to take in the face of an extreme threat.
My credentials are these: I have been a journalist for over 20 years and in the past decade have talked with well over a score of security experts about this exact scenario. These experts include two former SAS officers, as well as three retired Generals and numerous army officers, naval officers and security experts. This advice also accords with the very latest guidance from the National Counter-Terrorism Security Office.
And they are all of them are saying the same thing: never, ever do what an Isis terrorist wants you to do. And that is because he does not have your best interests at heart. He only wants one thing. He wants you dead.
Journalists are generally advised to steer clear of Nazi analogies. But in this case, the comparison is so exact that it's worth making.
The Nazis only wanted to do one thing with the Jews. They wanted to kill them.
But the Nazis - like Isis - quickly realised that a passive captive was a lot easier to kill. Hence the reason why many gas chambers were dressed up as showers, often with floral window boxes on the outside of the building.
It's much, much easier to shoot people if they're calm and obedient and lying on the ground just waiting to be shot.
What an Isis terrorist - or a Nazi soldier - does not want is dozens of people running and screaming and charging straight at them.
I don't want to sound too inflammatory.
This horrific terrorist shoot-out is almost certainly not going to happen to you. Frankly, you're probably more likely to win the lottery than to be caught up in an ISIS shooting.
However, given that it's sometimes best to know what to do in a worst-case scenario, this is what you need to know.
And if even one person reads this article, and takes it on board, and then perhaps, just possibly, saves their own life, then that is one hell of a result.
Here are some other things you may want to bear in mind.
* The moment you hear gun-fire, you want to get running. If it's close, then you're diving for cover. If it's in the building, then you want to be running for the exits. And - just like when you go onto a plane - it's always a good idea to have registered where the exits are beforehand.
* If you can't get out of the building, then hide. But bear in mind you'll probably be better off outside the building. This may mean diving clean through a window, and you may end up with some savage injuries; this may well be better than the alternative.
* The first few seconds are the most important. Everything is still in flux. This is your best opportunity to do whatever it is that has to be done. Once they've got you all on the ground, or herded into a slaughter-room, then your options are much more limited.
* Some people can actually run in high heels. Most people can't.
* If you've got a bag or a rucksack, then that's a weapon. You can swing it, you can hurl it.
* If there are fire-extinguishers to hand, then use them. You can fire them off, you can hurl them, you can use them as a bludgeon.
* If you're in a confined space, like on a train, pull the emergency cord. Smash the windows to get out. It may well be difficult to get away from a gunman. And therefore - if you're brave enough and can think lucidly enough - your best bet may be to go for the gunman. What terrorists do not want is close quarter fighting.
* The terrorists have probably been trained in how to use a gun. They may be less capable at hand to hand fighting. If they're near, your best chance may be to close in quick. It's not a great scenario. Nothing is a great scenario if you're confronted by a drugged-up terrorist. But it may be your best chance.
* Closing with a gunman may also give other captives a chance. Of course no-one wants to be taking one for the team; you'd rather survive the whole horrific ordeal. But if you're a distraction, then some of you might get out alive - as opposed to all of you winding up dead.
* If you're with a group, then you can act together. Together you are a much more formidable threat. If you all throw your phones or keys or bags, if you all move at the same moment, then some of you - some of you - may get out alive. With luck, you may swamp the gunman before he's killed anyone.
* Absolute, absolute last resort. Playing dead. If you're going to pretend you're dead, you're going to have to smother yourself in blood and contort your body into a wholly unnatural position.
* Above all: if you are trapped by gunmen, then... Whatever They Tell You To Do, Do The Opposite! Do not be passive. Do not "calm down". Move - and move fast, and if you've got nowhere to run, then run right at them!