William Easterly in VoxEU:
The “tipping point” is a popular concept covering a whole range of phenomena (and a best-selling book by Malcolm Gladwell) where individual behaviour depends on the behaviour of the herd.
Its original application was to racial segregation. Nobel Laureate Thomas Schelling developed a beautifully simple model for this. Suppose that whites have different degrees of racism – some would “tolerate” higher shares of non-whites in their local neighbourhood than others. Schelling showed that even the less racist whites would still wind up exiting during tipping because of a chain reaction.
Here’s how it happens – at first only the most extreme racist whites exit. But their departure causes the white share to go down, making the second most extreme racist whites uncomfortable, so they also exit. The white share goes down some more, and so now even less racist whites will be uncomfortable being a white minority, and they will wind up exiting too. So the remarkable prediction of the tipping point model is that just a little bit of integration that directly bothered only the most racist whites wound up causing all of the whites to exit. So even if the typical white were perfectly happy with an integrated neighbourhood, these neighbourhoods would be so unstable that the final outcome would be extreme racial segregation. The segregated non-white neighbourhood will remain permanently non-white. Segregated white neighbourhoods (with a white share above the tipping point) will also be stable, because virtually all whites will tolerate a very small non-white share. So segregation happens through a chain reaction, even though the average white person did not want such extreme segregation.