Think about this for a minute. Why would the Navy take one of its brightest bulbs and toss him in the bilge just because he didn't make it through their toughest academic program? Well, if he was a lazy slug who distinguished himself not at all during his "audition". That would do it.
There are two parallel sets of standards by which you will be judged during your nuclear training phase. 1) Your grades. 2) Your level of commitment toward your assignment.
Your grades can make you a nuke, or an ex-nuke candidate (a drop). Your level of effort and dedication to the duty that is assigned to you (study hard and long) may or may not be an issue. If you pass the course by breezing through it with no effort at all, you will still be a nuke. If you bust your ass and pass, again you will be a nuke. But if you don't pass, that is when #2 becomes the more important standard. A drop who consistently put in as many hours as humanly possible, participated in the classroom, sought out instructors , formed study groups, etc. will get prime consideration for orders over the guy who put in 10 hours a week with an average just above passing until it got hard then kicked it up just a little too little and a little too late. Of course, even he will get better orders than the guy who just gave up, or spent all his time at the beach, or gave excuses why the work was too hard for him though he frequently skipped study hours or did the bare minimum hours.
The point? If you are sure that you will fail, try harder. If it is hopeless, still try harder. If it is a sure lock that you will pass, try even harder still (you never know what is going to be on the comp). Lots of guys got half way through with their brains tied behind their back. When they got into the deep end, and couldn't cut it anymore all those hours they didn't put in during first half came back to haunt them. Yeah, a 3.8 on a test is good, but a 3.85 would have helped the average more when it became a problem later. The lack of logged hours early on will reflect badly if you fail by a hair in the end.
The people who matter will notice the difference. There is some pretty decent duty for nukes who were academically dropped but gave good effort. What you do on day one will still matter six months later, but by then it will be too late to go back and put the time in.
Just remember, this is NOT college. Passing or failing is not up to you. Your duty is to study and learn. You do your duty and the result is secondary.