The so-called science of poll-taking is not a science at all but mere necromancy. People are unpredictable by nature, and although you can take a nation's pulse, you can't be sure that the nation hasn't just run up a flight of stairs.
E. B. White (2011). “In the Words of E.B. White: Quotations from America's Most Companionable of Writers”, p.165, Cornell University Press