It really depends on what you're reading. You can take a great many non-fiction e.g. social science books and stick to the introduction and conclusion, plus som

It really depends on what you're reading. You can take a great many non-fiction e.g. social science books and stick to the introduction and conclusion, plus some skimming of what's in between, and still grok the general gist of what's in there. Not saying you get full comprehension - far from it. But you'll get a lot of it because it's massively redundant, especially if you're familiar with the underlying patterns and heuristics (which I'd argue are largely grounded in experimental social psychology).