Dramatic overthrow of long-reigning political regimes, thoughts, and beliefs are often precipitated by some seemingly insignificant precipitating spark. Yet before the sudden overthrow, it may be difficult to detect any public sentiments in favor of such momentous changes.

Such an apparent paradox is quite understandable because publicly expressed preferences are often falsified when the true private preferences are contrary to prevailing public sentiments. Thus, social pressures can make people say that they want and believe something that they really don't want or believe. In a communist regime for example, almost everyone may talk about the enormous wisdom and virtue of the leaders of the Party, even though almost everyone thinks that the leaders are scoundrels and fools.

Because private preferences are forced underground, there is no easy way for individual dissidents to gauge how widespread the opposition to the status quo is. But since falsifying private preferences exacts a psychic toll, the dissidents yearn to express them when they detect a threshold critical mass of fellow dissidents. When the threshold sequence¹ of individual dissidents are sufficiently close together, a precipitating spark will set off a revolutionary bandwagon (i.e., domino effect) of dramatic reversal of the status quo.

While private preferences may overthrow public preferences, public preferences may also transform private preferences over time. For example, certain private belief may get lost or abandoned as the content of public information changes over time. If certain thoughts are “unthinkable” – in the sense that people who entertain them are seen as uncivil or immoral – they may eventually become “unthought”, that is they disappear altogether. As this happens, people become less conscious of the disadvantages of what is publicly favored and more conscious of the advantages. In the long run, private opinion itself moves against the thought that is publicly disfavored. If one has never heard that women should be equally educated with men, or that caste systems offend equality, one may well not think of these things at all.