"Fundamentally, stock markets are driven by popular narratives, which don’t need basis in solid fact. True or not, such stories may be described as “thought viruses.” When they are pernicious, they are analogous to the Ebola virus: They spread by contagion."
So potash fertilizer price has nothing to do with supply, demand, transport costs, etc. It has to do with the strange occult doings at the Hogwarts School of Witchcraft which are spawning a collective consciousness. May be the phase of the Moon too affects the market (pic). Shiller is a Nobel Prize economist.
N.B.: Do I smell the Frankfurt School in Shiller's argument? But he is apparently of Lithuanian descent.