Terrence Tao commented of internalizing [here: https://terrytao.wordpress.com/career-advice/does-one-have-to-be-a-genius-to-do-maths/]
"It is true that some mathematicians can be vastly more efficient than others at learning material, but I feel this is more due to experience and an efficient means of study than to any innate genius ability, though of course innate talent is still a contributing factor. For instance, among the graduate students I have advised, the first paper they read in a subject often takes a month or so to read (and they have a question on almost every page on the paper); but after a few years, they can get the gist of a new paper in the subject within a day, skimming past all the “standard” (or at least “plausible”) portions of the argument and focusing on the key new ideas. The key, I think, is to find one or more efficient ways to internalise the subject – either by using formalism, or geometric intuition, or physical intuition, or some other analogy or heuristic. Each mathematician has their own different way of doing this. Ramanujan, for instance, apparently performed a tremendous number of numerical computations, and derived much of his intuition from the patterns he observed from those computations. The intuition wasn’t always correct (for instance, he famously gave an incorrect formula for the n^th prime), but he did discover a number of amazing results this way, some of which took a long time to prove rigorously."
I could not make any sense of what's written in the bold letters (not the literal meaning, of the methods). How one does that ?