Counterpoint example, I've yet to do grad school but I did take some graduate level classes as technical electives my senior year. While they were the most interesting in the abstract, the professors that taught them also seemed to assume that interest alone will drive you and you therefore need less structure. I found this lack of structure extremely annoying and difficult to mange, expectations were always vague. What's the point of the professor if I have to define everything myself? I ended up saving everything to the last minute as my more structured undergrad classes demanded more immediate milestones, which just produced a ton of stress and some shock when I ended up with a B in Compiler Design when I was hoping to just barely scrape by with a C- or something, given the relative lack of time and effort I'd put into it.

Taught me that I'm just not well tuned for academics or pure research. I'm extrinsically motivated, I need a real-world problem to anchor to, and if that problem requires me to learn Brainfuck then I'll enthusiastically learn Brainfuck, but I would never learn Brainfuck for fun.