Of course soldiers come try to come up with an understanding of the battlefield, but name me one army on earth that says aloud to their fellow soldiers and commanders "The theoretical is ____, and the practical is _____". There isnt one. Again if we are going to compare the ultramarine to any modern army it would be the Canadians or the Brits for their supreme training.
Not in so many words. That's putting a grand sounding name on it.
Considering that FPGRM was based in Arbroath, as in, the UK's nuclear submarine base, and the single greatest threat to any "theoretical" Russian invasion of the land, it was customary to have various plans and contingencies, with back ups for if they failed.
I can't tell you the number of times (seriously, I can't, it's a legal thing) when I've fished out Special Boat Service personnel performing a probe on our defence, or caught Special Air Service parachuting in, or any other various numbers of "random passersby" who "just so happen" to have ended up taking a picture in a spot that's not particularly helpful to security.
These happen from learning via experience of doing them wrong, but from people saying "what if".
One of the things that really fucking annoys me about Know No Fear is that with the exception of a single marine that no-one envisages having to attack other legions; considering the Space Wolves background, and the World Eaters, and the role that the previous 2 legions, as well as presumably the fate of the Thunder Warriors, not having any concept of attacking another (especially as they train against one another too) legion is fucking preposterous.
Dan Abnett isn't as bad as Graham McNeil for using that as a story device, but it's a pretty large plot hole/fridge logic moment that bears explaining as to exactly WHY something like that is the case.