Good question. Look at all that's been put into print in just the past fifty years and wonder if originality remains an option.
A study for someone else to do - you can earn a PhD at the same time. I'm an idea man - someone else can do the work. Has anyone ever examined supervised in-class essays for signs of plagiarism. Perhaps this could provide a lot of ammunition for defence against a charge of plagiarism. In a narrow field there are limited methods of expressing ones self and maybe duplication of phrasing could very well be honest.