New soldiers have no idea what to expect come day one of basic training. They may think they’re ready, but these Drill Sergeants are there to prove otherwise.
As a new soldier, day one is very intense mentally, and recruits have to be on point or they will be having some trouble.
The Drill Sergeants’ job is to train soldiers with discipline and aggressiveness, to get them ready for combat. When that time comes, there won’t be anyone around to train them.
This is stage one of becoming part of the United States Military.