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I think it's a learned skill. It's a judgement call. As a general rule students should restrict their direct quotations in a History essay to primary documents, if they're working with them, and then just the best bits. And really make a point that you are developing. For secondary works, especially, really only quote something that is unique or original to that work or that is colourfully or memorably put. There's absolutely no point quoting a line that says, "Wheat production went up for the next decade." Put that in your own words. You have to cite that information. I think students have this idea that if it isn't between quotation marks they not only don't have to cite it but they shouldn't. But, in fact, you've got to cite it but not quote it, quite often. That takes practice. The other thing to remember, I think, is that these quotations don't do all the work for you. You shouldn't just drop it on the page and expect that the reader will understand exactly what you mean by it. Spell it out, introduce it, contextualize it, and then provide some analysis to follow up.