Some confusion on bell curve … C’s should make up a good percentage of your grading if you use like mean+/- one standard deviation.
http://www.fctl.ucf.edu/TeachingAndLearningResources/CourseDesign/Assessment/grading.php has the bell curve and some other grading methods. Here the average score is the divider between B and C.
As and Fs rarely affect the grades of most students.
Probability theory can get pretty complex, and I am not a statistician. But in a large class, many times there is a bell curve shape to the raw scores. Professors who teach a lot and give sort of similar tests will get the same distribution year after year. They can still choose to decide whether 1 SD is the right breadth of the C or B/C band and if average is a C, a C+ or a B. And, if this years class is smarter than last years, maybe they will give more Bs and As (I would argue maybe they should). And yes, sometimes a problem is just too hard, so you either toss it out, or it just floats up there as the magical difference between a 80A and a 100A.
The 3 problem test projected above can be turned into a nice bell curve if you put just the right number of basic, advanced, hard problems on the test.
And despite students hating this idea, the bulk of people in a class fall right on the part of the curve where you expect them to, based on ability, effort, and engagement in the class. Lots of effort can make up for ability, unless you just start out too unprepared.
One myth that also leads to disappointment is that there are a lot of people with high ability that don’t do much work. Typically that is not true (maybe one or two people per class), so people of medium-high ability feel they deserve a B when they really deserve a C. They are not only not as able (prepared, gifted, whatever) but not working as hard as the As and Bs.
And honestly, at some point in your life you need to be able to think critically and solve problems that are not exactly like what you have been taught. It is hard to justify a high wage for someone who needs to be walked through their work (I guess by someone “smarter?”) and stumbles when asked to do something new. The world changes too, so what you learn in a formal setting can only take you maybe 10 years past college. Past that, you need to be able to extend yourself … and also to teach yourself (which is also an issue if the professor is no good or whatever you blame for your lack of comprehension).