I have a rule that has helped me a lot in life, particularly in my education: If there is a book I am interested in, I buy it. Regardless of the cost. Regardless of whether I have a stack of other things to read. Regardless of whether I have any sort of certainty about whether it’s any good. If I want it, I buy it. And when I buy it, I don’t care how much I spent on it or how rare it might be. I treat it just like every other book (which means marking up and writing in it).