A common issue I see in student writing is how they allow substitutes for their own thinking. It could be an online resource, a long quote, or the textbook itself. Some students vaguely re-write the chapter, following its contours in their own words. Others include a large block quote and do not comment or examine it; instead, they put it out there and move on. Preachers do this as well when they have long quotes from books or poems. Primary and secondary teachers are also tempted by this as they provide resources to students and parents.
There really is no substitute for clear thinking in your own words. It’s been said before: be a voice, not an echo. Citations and resources should support your own ideas and analysis. It’s really hard work, and that’s why we’re so tempted by the endless resources of the internet to use someone else’s thoughts (or even plagiarize them). It’s just like dieting. Pills and magic cures are great, but the clear path to weight loss is burning calories while controlling our eating. It's so easy to get overwhelmed by great ideas and quotes in a book or webpage, but the clear path to thinking and writing well is learning to think clearly in one’s own voice.