One of my friend said to me "when I was an undergraduate student, my professor always told me not to be a cooked book. A cooked book means memorizing everthing in studying. Rather, alwaying thinking intuitively is necessary"
By accident, the professor who taught my friend knew a professor who are teaching me and the friend. They belonged to a same university PhD program. Then, the professor of our current class routinely explains "the intuitive point is..." even in a course of complicated mathmatical formulas.
Considering my past, one of my failures in my youth age was overly emphasizing memorizing contents of textbooks and abolishing understanding contents. Of course, memorizing everything was impossible for me, thus I got nothing from my study time. Strictly speaking, I wasted my time...
If I had met an advisor as my friend met, I would have got more....
Recently, even a can of beer makes me drunk...I might be too tired.