The problem is that if you approach learning in this way, you are just going to totally fall apart in grad school. The first thing that you need to seriously ask yourself is why you want to go to grad school in the first place. Part of the problem is that after the first two years, no one tells you what to do and you sort of have to figure it out on your own.
I've seen it happen that people that just ace tests get into grad school, and after the first year or two, they totally fall apart. Getting your Ph.D. is probably one of the most intense and brutal intellectual experiences that you have to go through,
It actually depends. Many successful profiles among mathematicians spent a lot of time acing classes as undergraduates, along with some time afterwards learning independently about topics of interest, and the primary thing they did was enter into more advanced coursework, where the nature of thinking is much more akin to what you do in the PhD. I made the distinction between theoretical and less theoretical fields for a reason.
These mathematicians also tended to think deeply about what kind of material they enjoy. But realize that even upon entering grad school, in some fields it is typical to spend a year or two once actually in grad school figuring out what one wants to do.
Acing (advanced) classes combined with a penchant for being thoughtful about what you want to do is ultimately the combo often needed in theoretical fields.
Remember, acing advanced classes isn't the same thing as playing a game, typically they can make these courses ones designed to give one the tools to start being a researcher in a field. It depends on your field and how much there is a discrepancy between classes and research -- I know many computer science students who hardly care about classes at all, because classes simply don't matter to them.
If you don't have ultra-developed maturity, then you just shouldn't go out for a Ph.D.
I'm inclined to completely agree, but the reality is that most people are incredibly stubborn. However, these people often end up in graduate programs that let them spend a lot of time figuring things out, and may be less demanding. I discourage these types from even pursuing the PhD myself, but reality says that they won't listen. As many of these people also exit college with limited, very theoretical skills, it's in their interests to at least ace their basic classes, as that tends to get them somewhere so they can figure things out, or they tend to really mess themselves up.
Reality also says a lot of people reading this forum probably belong to this category. A lot of people just set themselves up thinking they're going to graduate school. At the very least, I'd hope they get into a master's program (especially since people with poor planning should not, in my opinion, pursue a PhD). Then they end school with no internships (because their field is theoretical), a somewhat bad GPA because they did what interested them without working the system enough, and fewer opportunities than people who're intellectually a lot less curious and a lot less smart.
I think as long as one has a
plan in mind, and is very smart about things, you don't have to listen to words like "the real world just cares about exams".