For Fisher, the years 1929–1933 were extraordinarily trying. He was totally unprepared for the onset of the Great Depression. The lesson of the theories he had worked out in the 1920s seemed to be that significant fluctuations in economic activity were preceded by changes in the price level. But that model could not explain what had happened in the American economy following the stock market crash in the autumn of 1929. For the preceding half decade or so, the general price level had been remarkably stable – a condition that appeared to have augured well for continued economic stability. Fisher – along with a substantial number of his professional colleagues – confronted a formidable intellectual challenge in meshing his theorizing with observable realities.