What if I get B's in my first semester in graduate school (engineering program)? Why is getting A's so important? 

What if I did not have the background to pursue graduate education but nonetheless I decided to enroll in a graduate program? 

I am in graduate school. I got straight A's at my local university (undergrad studies) and was admitted to the graduate program in engineering by one of the Big Ten universities. I am working diligently and extremely hard, and I have come to realize that the preparation in math and engineering from my undergrad institution was not even close to the preparation that students at my current institution have received. 

I neither come from a research background nor have a strong mathematical background, but I am responsible and can learn the material so I know I am smart. However, my previous engineering school could have done better at training us as engineers, I would say that our engineering classes did not developed our problem solving skills and/or analytical thinking which is something I tried to learn on my own. I did what I could to learn what I believe had to be taught to me, which is why I was accepted into my current institution. 

But it is so frustrating to feel the difference in knowledge and problem solving skills that other students seem to have just because they were instructed better. Currently I am getting B's for my graduate classes, and it is my first semester. So I would like to know, do grades really matter? Should I drop out after all of this hard work? What about the ones like me who want to have a better future and pursue grad school but did not have all the opportunities and sufficient preparation but can still do good, maybe not getting straight A's right from the beginning but definitely later (which is what I am aiming for and I know I can do it). However it is a bit discouraging, when all I find on the internet is "B's are like C's in graduate school" that statement seems to be unfair for people like me who work hard on school and research.
Ultimately, your grades as a graduate student matter very little, except for:


A handful of employers who have GPA requirements for graduate programs;
Fellowship programs, which may require a GPA minimum;
The academic regulations, which may also specify a GPA minimum to continue in good standing.


However, it should also be noted that most graduate courses are based on the premise that a grade lower than B is a failing grade. Therefore, it's better to get A's than B's in graduate classes. But, at the end of the day, having B's is probably not going to impede your career much—especially once you enter the working world.