Crashes and collapses are generally non-linear events. They are hard to predict and depend on crowd response. People in the prediction business tend to throw out lots of them and then point to the happenstance where they came true. Occasionally, you have the orchestrated crisis. George Soros collapsed the French franc and profited mightily. After the battle of Waterloo the British stock market was collapsed, apparently on purpose, by the untrue rumor that they’d lost.
I’m increasingly under the impression that a full blown market crash can’t happen.