I wrote an editorial some time ago that's been published in several places.
Through the discussion of two seemingly unrelated topics (stomach ulcers and global warming), my intention was to point out the potential risks of being "absolutely certain" about any point of view.
A friend recently sent me a link to a story from The Economist about the particular bacterium that I discussed in the editorial, Helicobacter pylori. As it turns out, using antibiotics to rid the body of these little critters might help you avoid stomach ulcers, but doing so may then lead to other adverse unintended consequences. (PDF (204 kB) of story)
So in short, what we originally thought to be true was overturned by something seemingly preposterous and ridiculed by those "in the know", to be then accepted as a new version of truth, only to be overturned once again by something that was previously unconsidered. Which is to say...my point exactly.
No matter how obvious or certain something may seem, there's always a possibility that it's completely wrong, or right, or something in between. The only thing I'm ever absolutely certain of, is that nothing is absolutely certain.