The physical world has some wondrous characteristics. If you have two pens, one white and one black, and believe that the white pen will drop more rapidly than the black one - neither pen cares a whit for your belief. They fall as they fall and your silly belief about the importance of color has no influence over their behavior.
By contrast, the social world doesn't so neatly defy expectations. Most of you will have heard about the teachers who were told about promising and not so promising students at the beginning of the year. They were told that some students had scored very high on a test indicating potential and that they, the teachers, should show more patience with those students, do more to encourage their performance, and, quite simply, expect more. Given that others had scored poorly, the teachers should not expect as much from them. As it turns out, the predictions were accurate. The problem? The students had been divided into the two groups randomly. This kind of predetermination happens outside of the classroom as well.
If a critical mass of the community believes that you are less human, there will be plenty of evidence to support this claim. The pen is not influenced by your beliefs about its performance; the individual within a particular social milieu is greatly influenced by social beliefs. To consider the power of changing beliefs just remember that Christ referred to the adoption of new beliefs as being born again.
This is the dirty little secret that liberals won't admit: the data that supports the racist claims of books like The Bell Curve is factual. There is evidence that blacks have lower IQs, just as there is data to support lower life expectancies, lower incomes, and higher jail rates. These differences may yet prove to be genetic, but such a claim seems highly suspect. The genes that control skin pigmentation are so minimal within the arsenal of human genes that the probability of their influencing intelligence, income, and incarceration seems questionable if not absurd. The problem with past data is that it tells you nothing about future potential.
This was the genius of Martin Luther King. He spoke to latent potential. Rather than dryly citing facts about what the data suggested, King spoke to the human spirit.
I think that Jacques Barzun articulated this difference best:
“[T]he very point of emancipation … is not to give power to those who have earned the right to it, but to lift the helpless to a level where they are free to learn how to use the right.“Those who oppose freedom argue that as illiterates, as slaves, as children, they cannot manage the household, which is true though illiberal. The political history of the West has been a running battle between the ‘realistic’ deniers of one freedom after another and the generous ones who gambled on another truth, that capacity is native to all and depends only on fair conditions for its development.”
Martin Luther King’s appeal came from so many sources. One is the realization that our own potential is not seen in our past, regardless of our race or situation. And that is a reminder that all of us could use. Happy Martin Luther King’s Day!
 Jacques Barzun, From Dawn to Decadence: 500 Years of Western Cultural Life, 1500 to the Present (New York: HarperCollins, 2000) 534.