Meanwhile I never specifically study for a test. I've just studied regularly every day, thought about these things regularly, let my subconscious do some heavy lifting, and built associations in my brain that help me derive equations or fill in gaps if needed. For my effort, I've got a ~3.9 GPA and all kinds of free time for dating, exercise, hobbies, and teaching myself useful skills in my field that university isn't teaching me.
I think the core problem for most people is that they are attached to the wrong outcome. Their goal is the high GPA. My goal is grokking material and making myself useful; high GPA is almost a given (and frankly redundant) after that, and the only difference between my 3.9 and a 4.0 is the tolerance for BS and busywork... and about a gazillion extra hours of work.
It is, of course, understandable, because people think High GPA -> Good Grad School -> $$$$. But I suspect, and your story confirms, that "Reasonably High GPA" + "An Actualized Human Being Who Is Not a Robot"[0] -> Good Grad School -> Richer Life + $$$$.
[0] - Not trying to denigrate those who take the other path, but I see them miss out on a lot of life and ultimately not be as developed and awesome as they could be. I'm saying these things not just about random strangers, but also about people I know and love. They've optimized primarily for passing tests.