Markets are heavily determined by emotions, so calling it smarter than you or I, is akin to believing that our emotions, sans reason and logic, are better than our collective knowledge.
"Rationality
Rationality is defined as "the ability to reason" and "to exercise good judgment." Humans of course possess these traits, but they are not the ultimate driving force behind human behavior. One of the basic facts of modern psychology is that our intellect serves our emotions, not vice versa. Human behavior is not primarily the result of logical cost-benefit analysis, but of emotions like love, hate, loneliness, fear, greed, anxiety, sexual attraction, pleasure, pain, etc. We use our intellect only to fulfill or avoid these emotional states.
Let's consider the first half of the definition of rationality: "the ability to reason." Just one example of how emotions are irrational in this sense is sexual attraction. We do not "decide" or "think" to become sexually attracted to someone; we just are, thanks to our genes and hormones. The only role of the intellect here is to formulate a mating strategy.
Now let's consider the second half of the definition of rationality: "the ability to exercise good judgment." Just one example of how emotions are irrational in this sense is self-destructive behavior like alcoholism. People become addicted to alcohol because it chemically induces an emotional state: euphoria. But while pursuing this emotional state, alcoholics destroy their lives. George Vaillant is perhaps the nation's leading authority on alcoholism, and he offers the following portrait of an alcoholic's career. Most alcoholics go on and off the wagon, but their condition progressively worsens as they reach middle age. They will generally lose everything dear to them: their family, their friends, their jobs, their homes, their possessions, their reputations. Finally they will hit bottom: they will have nothing left to lose but their lives. This is the turning point for most. Roughly a third will die or stay in horrible shape at the bottom, another third will become abstinent, and another third will shift to more responsible social drinking. (1)
Although one might argue that most alcoholics ultimately do the rational thing at bottom and choose survival, the point is that the 20-year slide to the bottom is not rational in the first place. Losing a job would be a negative incentive that would compel a truly rational person to stop drinking. But the alcoholic goes on to the next negative incentive -- losing one's family -- and then on to the next -- losing one's house -- and so on, without ever making the obvious rational choice. And all in the pursuit of an emotional state.
A large part of the reason why alcoholics aren't rational is because they are in denial. In other words, they've constructed their own alternate reality to protect themselves from the ugly truth about their condition. For instance, they often blame everyone else for the negative events in their lives, when in fact people are just reacting as they normally would to a problematic person.
This sort of irrationality (or "rationalization") is not isolated to alcoholics. To varying degrees, we all rationalize our reality. The consensus of modern psychologists on this point is overwhelming, and finds its best expression in Cognitive Dissonance Theory, first advanced in 1957 by famed psychologist Leon Festinger.
A "cognition" is a belief or attitude. "Dissonance" is an inconsistency between cognitions, or between cognitions and actions. For example, dissonance occurs when you hit someone (say, on a regular basis) and then feel guilty about it between times. Dissonance is unpleasant, so people seek to reduce this unpleasantness by changing either their behavior or their cognition. In the above example, you could either stop hitting someone, or else stop feeling guilty about it ("He or she deserved it"). Most of the time, it's easier to change one's beliefs than behavior, especially when the behavior is addictive, pleasurable, genetic, etc. Psychologists have concluded that people create rationalizations or justifications for their beliefs and actions to maintain psychological stability -- they do not generally come to those beliefs or actions through objective rationality and self-interest. (2)"
Myth: Homo economicus is a valid assumption