I know of some farm boys who were drafted into the military and when it came time for rifle qualification these boys all qualified immediately by placing all their shots on target in accurate manner. They were qualified in the few minutes it took to fire the required number of rounds. But the urbanite boys could not hit the target at all. They were firing away all day long and had no comprehension about ballistics, trajectory or sight adjustment or aiming or what makes a projectile hit the target. The farm boys who qualified immediately were sitting there for hours as the urbanite boys were firing away all day long and consuming large amounts of ammunition (without hitting the target).
A farm boy is typically trained to be multitasked. They can do carpentry, welding, working cattle, veterinary work, mechanics, shooting, trapping and a long list of other things. Rural boys have learned to do things for themselves because farmers and ranchers typically do not hire outside help for most of their work. The manner that a farm boy learns these skills is by mentoring as he follows his father on the farm and the father does these tasks together with his son. It is for this reason that a farm boy is trainable because he has a wide breadth of experience and when these boys go to the military they can easily pick up on tasks like shooting. Farm boys typically have started off shooting with home-made slingshots, then BB guns, then pellet guns, then a .22 rim-fire, then shotgun and then center-fire rifles. All of this experience from their youth prepares them to be able to easily qualify on a military rifle. Urbanite boys may grow up doing little more than playing video games or throwing a ball through a hoop. But none of these type of activities will prepare them for doing anything useful in life.
In Vietnam the US military had a big shortage of helicopter pilots because there was no other means of moving men and equipment over the vast jungles except by these aircraft. It was the rural boys who were typically selected to be trained as chopper pilots because they were said to be “trainable” and this means that they had a wide range of experience prior to coming to the military that enabled them to catch on easily to new concepts. The more experience a boy has, the more he is able to understand and comprehend new tasks presented to him. It was because of this wide range of experiences that farm boys could catch onto the instruction given them easily – (while the urbanite boys were like a cow staring at a new gate)! This expression means that they are totally bewildered! A cow that sees something new will just stand there and stare at it not knowing what he is supposed to do. So this expression describes someone who is at a loss of what to do next and has no basis of past experience to help them comprehend any new situation they now face.