If you(general usage of you) can’t handle someone yelling at you and trying to make you lose it in a somewhat safe environment, you’re probably not going to do well when people who hate you are trying to kill you in the middle of a battlefield.
Folks don’t realize, the abuse is meant to mentally prepare you for folks trying to kill you.
During Desert Storm I saw an interview with a soldier who stated that he had hated his D.I. during training but he now realized that he might not be alive had he not been trained the way he had been. I was astonished that the MSM reported it verbatim.
Something lost over the generations was the intent of the harassment package.
When the US went into total warfare, as in WWI and WWII, every able bodied man wore a uniform.
Not every able bodied man, though, had the faculties to perform in combat as infantry.
There does exist a percentage of the population, when faced with adversity, tends to physically freeze up, dwelling instead by spiritual devotion. This particular trait isn’t volitional, other than remaining in fellowship with God, but it is associated with particular spiritual gifts not given to all men.
Boot camp was the initial screening mechanism to better identify these traits, amongst those who sincerely sought combat roles. The introduction to adversity and stress inducing environments helped identify those who tended to freeze up under combat environments, so they wouldn’t be improperly assigned to direct action line units.
The harassment packages were also used to further condition all personnel to a common training experience, forming an espirit de corps and camaraderie amongst enlistees. It also helped assess proclivities of the individual with the needs of the Corps.