My son enlisted in the Navy for the Advanced Electronics Career Field and successfully completed 9 weeks of electronics training, followed by the A school for his Fire Controlman rating and then his weapon system C school. It was a pretty demanding set of schools academically--especially the initial electronics course.
Throughout the entire process, everyone in his cohort knew that failure to continuously meet standards would result in washout--and being sent out undesignated--assigned to a permanent station/unit, "needs of the Navy". It was a pretty powerful motivational tool, lol. Nobody wanted to end up undesignated--chipping paint with the deck division, or handling garbage with ship services.
Don't get me wrong, every job on a ship is important in one way or another. Some are just more appealing than others?