A 1900 doctoral thesis argued stock prices are basically unpredictable

French mathematician Louis Bachelier's 1900 doctoral thesis modelled stock prices as a random walk, where each day's price change is independent of the last and no pattern in past prices predicts the next move. His examiners were unimpressed and the work was largely ignored for fifty years. It resurfaced in the 1950s-60s as the mathematical backbone of the efficient market hypothesis, and was popularised in Burton Malkiel's 1973 bestseller A Random Walk Down Wall Street.

— Louis Bachelier, Theorie de la Speculation — Doctoral thesis, 1900