Thanks for the pointer to Peter Sarnak's advice. I believe this is the history of ideas advice you were referring to on pg 1008 (1031 in pdf): When learning an

Thanks for the pointer to Peter Sarnak's advice. I believe this is the history of ideas advice you were referring to on pg 1008 (1031 in pdf): When learning an area, one should combine reading modern treatments with a study of the original papers, especially papers by the masters of our subject. One of the troubles with recent accounts of certain topics is that they can become too slick. As each new author finds cleverer proofs or treatments of a theory, the treatment evolves toward the one that contains the “shortest proofs.” Unfortunately, these are often in a form that causes the new student to ponder, “How did anyone think of this?” By going back to the original sources one can usually see the subject evolving naturally and understand how it has reached its modern form. (There will remain those unexpected and brilliant steps at which one can only marvel at the genius of the inventor, but there are far fewer of these than you might think.)