Most undergrads have no idea where they will end up in life. I certainly could not have predicted the graduate programs I considered - none of them having anything to do with my EECS major.

Getting poor (or even average) grades closes many doors, especially in these days of grade inflation (at many, but not all schools).

Fair point. I had a plan and thought I roughly knew the requirements. I can see how students who are more exploratory would need to be more careful.

This isn't necessarily true. I had a 2.9ish GPA as an undergrad history major but I still got into a respectable engineering masters program (NC State) based on career merits. Granted, that was 10 years after I entered the workforce as a technical professional, but even so, there are many ways to reach any given end state, via hard work, excellent communication skills, and [hopefully] a strong network.

With excellent communication skills, and hard work, AND a strong network, you could get very far anyway.

Matter of fact those are 3 skills that are always in demand because anyone who possesses them can avoid truly coming to grips with the question in this thread: The necessity of good grades in determining your career.