This is only my opinion but here goes.
Yes a genuine Jack Knife happens under hard braking when the tractor gets slightly out of line (trying to brake and swerve together will make it far worse) it only takes a fraction of a seconds drive axle lock up and the weight of the trailer will whip it round in a flash.
Lets get one thing out the way, once a genuine hard braking jacknife starts there is little if any chance of recovery, (opposite lock etc is tosh, thats for acceleration or cornering oversteer slides which are mistakenly called jacknife’s…idiot traffic reports in winter about stuck lorries being jacknifed for example.)
There was a small chance of recovery at one time when Scania used to fit the trailer brake handle, going back to Scania 110 days here, if you lifted off the footbrake and applied the trailer brake only then it might just straighten up again assuming the trailer was loaded, empty trailer probably not going to have enough grip to stop it.
This is not to be confused with the Dead Man or secondary brake which works on steering and trailer axles only, the Scania trailer brake was in addition to normal secondary braking.
I had a Scania with trailer brake, in practice you’d be using it in conjunction with the footbrake regularly, not only did it balance braking well it helped cut down on tractor unit brake wear, if you were pulling A N Others trailer… 
It was an excellent fitment, needed care in use but a handy tool.
OK back to the modern lorry, and this my observed not engineering theory so i’m happy to be shot down in flames.
ABS is a good thing, as are modern brakes, but they are not perfect.
A lorry ABS does not perform as fast as a cars ABS does, you are dealing with compressed air and not hydraulics.
Air ABS systems cannot release and reapply the brakes anywhere near as quickly as a hydraulic system.
As such if a panic stop triggers ABS, it entirely possible that at the moment the tractor unit drive axle locks momentarily the trailer might already have locked up a moment before, therefore the trailer is shoving full weight at a locked wheel.
OK we’re ony talking milliseconds here, but factor in even a slightly out of straight combination and that millisecond can see the tractor starting to spin.
Does anyone remember the early ABS equipped trailers where ABS worked at all speeds, i’ve had trailers with particularly sharp brakes that the very second you touched them would lock up, re-application of braking took a second sometimes which feels like an hour, unfortunately the brakes would lock again and trigger another release etc.
OK thats done my theorising on ABS, probably all wrong.
Now to practicalities, its possible for drivers to lessen their chances of jacknife my setting their vehicles up properly and loading them better in the first place…not always possible i know.
I believe rightly or wrongly that the standard artic is safest when the tractor is loaded as reasonably heavy as possible obviously at or below its GVW.
I also believe that its best to get as much weight as possible onto the drive axle, less chance of it locking up prematurely if its imposing its full weight.
A bit of time spent setting the 5th wheel in the correct place for otimum loading is well spent.
I got a new tractor unit a few weeks ago, i have use of an axle weigher regularly and spent some time getting the weights exactly right…when it came the 5th wheel was too far forward putting more weight on the steer axle whilst leaving the drive axle light.
I could feel the uncomfortable imbalance on the road especially wet greasy corners, prone to too easy wheelspin.
Getting the weights right has made it handle much better, i try to do this on every vehicle i have had over the years.
Another benefit of correct 5th wheel positioning is to lessen the chance of oversteer slide on corners.
Loading.
If possible get that weight forward, an artic loaded so the trailer axles are up to max load whilst the tractor unit is 20% below its max is a jacknife waiting to happen.
I won’t get into good driving practice as you’re probably bored to tears already, such as allowing a braking distance and observing/assessing road surface condition and camber at all times, the good driver does this automatically.
Sorry the post has been so long, just my tuppence.
