I don't think you can know if you'll be great and go down in history, even after you achieve something, and some people who achieve great things don't go down in history (for a while, such as Alan Turing).
Do you think Tim-Berners-Lee went to CERN thinking he'd become a figure who essentially has shaped how we live every aspect of our lives today? I doubt it, I think he just thought, "oh, this would be pretty cool to have a go at, perhaps it'll even work." and coincidentally he achieved greatness.
You could make some spectacular historical discovery, reshaping how we believe human culture to have evolved, discover sentience in another species on this planet, or write a book which others happen to adore (as far as creating things goes, your always your harshest critic, and I really need to start listening to that statement I've preached for so long).
I too hope I may go onto great things, just see it as a goal, give it some structure (i.e. which field you'll become so great in) and try. If you fail, so what?