Revolutions happen because people have not been sufficiently flexible to adapt social institutions to changing conditions. Conditions may change gradually (feudalism is being replaced by capitalism; global climate change develops over the decades, etc.). But popular consciousness lags behind the change, and those who benefit from existing conditions (such as the feudal lords or the owners of oil industries) resist gradual changes. At some point there develops extreme tension between the existing consciousness and institutions and the need for change. Then there is either an explosive revolution or social disaster. The question is, why does it take so long, even when the need for change has become drastic, for there to be a major movement for the necessary transformation: for revolution?