Ubiquity: Why Catastrophes Happen by Mark Buchanan

     Build a sand pile grain by grain. At some point one grain will cause others to fall. At first only a few fall but overtime one grain can cause all manner of avalanches, big or small, depending on the history of the sand pile and its current structure. There can be a critical state where one grain causes a big effect but there is no big cause just a grain dropping in the wrong place.
     The author illustrates with examples from earthquake prediction, forest fires, evolution, historical events and more. Trying to predict big earthquakes or historical crises may not be possible. Extinctions may not have great causes but may be just the result of an event at the wrong place in the historical flow.