Leonardo da Vinci, artist, inventor and polymath wrote copious notes (many now reside at Windsor Castle for some strange reason). Among his ideas and sketches for inventions he wrote that everything has already been discovered, everything has already been done!
Which shocked me when you think of all we have discovered and invented since Leonardo's lifetime (1452 - 1519). I feel sure that one day we will look back at what we now know and howl with laughter at our present understanding of the world and the universe.
Edit: I actually have a great deal of affection for Leonardo because in my late twenties when I decided I was ignorant I thought I would start reading things that interested me. Art History was one of the subjects and Ancient Greece another. Soon after studying these subjects I reached my own crisis of conscience.