In my family, we have all pursued education to a master’s degree level at least. My older sister was first in her high school class and my younger brother was 2nd in his high school class. My younger sister and I were bums. My younger sister was in the top 10% of the class. I was not in any of these categories because I started very late. I believe that I was probably an attention deficit child, but in those days nobody paid any attention to this. I was first in the high school class for the last two years and I did in fact win awards as the best physics student, best chemistry student, best mathematics student, and best psychology student in my class. Because I had so much catching up to do I had to work doubly hard and this was very hard on me but did have the advantage of making me learn the core materials to the beginning of college very well. I do appreciate the value of pushing a subject to mastery rather than just meeting the requirements. In truth I found that at first I was having to really kill myself but over time it became easier.
Any subject which one studies hard enough to get an A will stay with him/her and help him/her in future studies much more than a course in which one only obtain a B. I believe in taking some subjects to mastery level. I am not sure that I believe that every subject should receive the same effort. I believe that mastery really makes the most sense for a course that is related to the direction you wish to pursue in your studies.
Obtaining very good grades can really be a help to a student. I have been deeply involved in college recruiting for my company and I know very well exactly how it works for my company and I can see very clearly the level of competition. I know there are years when we do not look at any resume below a grade point average of 3.7 for my department. Other years we may set the screening level at 3.4. These people also have to impress the on campus interviewer. If you are only a B student many of the more desirable and competitive employers will not interview you.
In times when the job market is tight it will be hard for you to pass the technical interviews. Many of the more selective employers are also the more stable employers and are better places to work. So I do not agree with just being a B student in graduate school at all. I would never have been accepted into Hewlett Packard had I not put up some very good grades.