As American author (and investor) Mark Twain famously said, history may not repeat itself but it rhymes. A century and a half later, many of his countrymen not only retain an appetite for speculation, but also a widespread belief that understanding the past can enable amateur punters to gain an edge in a stock market otherwise stacked in favour of pros. Tens of millions of dollars are spent annually on books and newsletters that claim to profitably time bull and bear markets.

Some, like the Elliott Wave theory, are so cryptic that they are hard to either prove or refute. Others are remarkably simple, pointing out recurring patterns even a novice can exploit. But adherents are learning the painful lesson this year that past is not prologue.