In the study of English Literature, many would argue that style and form are the only things one can differentiate. Over the course of the humanity's relatively minute history, our predecessors have written and spoken about virtually everything, leaving very little room for originality.
Of course, some would argue that there will always be more to say. Technological and scientific breakthroughs will smash through barriers of current intellectual capacity, expanding our knowledge, vocabulary and topical discussions. William Shakespeare, for example, would not have bragged to Ben Jonson about his recent high-score on Angry Birds, on his new iPad 2, or moan to his wife that there's a power-cut, preventing him from writing his next Tweet. Still, these are hardly the most virtuous, stimulating topics; perhaps all worthwhile subjects have been mined already for those ores of wholesome knowledge.
Still, it is no easy task to write original content. Even now, I am writing about a topic that has been written about and discussed for several years. The best many can hope to achieve is repeating what others have said, and reference it to avoid the minefields of plagiarism. Or, if one is particularly astute, perhaps an 'innovative' combination of someone else's idea with your own could present something in a new light.
My pointlessly pessimistic point is that one is unlikely to ever be original. The multiplicity of great minds have already mastered the main subjects of our time, and we can merely study and admire the expertly formulated theories of the great thinkers of our time, such as Newton, Shakespeare, Einstein, Watt, Plato and many others that I do not have the time or knowledge to fittingly acknowledge.
Brilliant post. Very true thoughts on our lack of originality!