It's a common misconception that an efficient market must be a random walk — the actual condition is that it's driven to be a martingale, where the EV in the future is equal to the current value. This

It's a common misconception that an efficient market must be a random walk — the actual condition is that it's driven to be a martingale, where the EV in the future is equal to the current value. This market is a classic example of such non-random walk martingale behavior.