Others will jump in to say that markets are not predictable like chemical bonds, but i would counter-argue that they should be more predictable and less fear-and-rumour-driven
A great quote from Galbraith is appropriate here. "The markets can stay irrational a lot longer than you can stay solvent."
I don't know exactly what you mean by should but whether or not fear and rumor should drive markets the fact remains that they do sometimes drive markets.