"There should be more or less of a jumble in your head or on your note paper after the first time and even after the second. Much that you will think of in connection will come to nothing and be wasted. But some of it ought to go together under one idea. That idea is the thing to write on and write into the title at the head of your paper. One idea and a few subordinate ideas - [the trick is] to have those happen to you as you read and catch them - not let them escape you. The sidelong glance is what you depend on. You look at your author but you keep the tail of your eye on what is happening over and above your author in your own mind and nature."