In fiction, taking ideas (hero's journey, middle earth, etc)[1] and adapting to a new story/characters is totally fine without attribution. There's probably only like 5 stories ever that just keep getting re-written this way.
But in non-fiction, academic research and the like, stealing ideas without attribution is a problem, because ideas are the whole point. Nobody reads a research paper for the plot.
But in school, and especially with non-fiction, we're so often told to "just re-word it to make it your own" which is actually the most insidious form of plagiarism. If I get an idea from you and want to include that in my paper, that's great, but I have to give you credit. Great non-fiction books I've read are riddled with citations and have 100-page bibliographies. The value of the book/paper is (often) in the synthesis of those ideas into something new, with maybe it's own ideas added on top. But "re-wording" does not make and idea your own, and does not escape a charge of plagarism.
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