To what extent was idealism about american prosperity and the american dream responsible for the crash? how did the idea of "rugged individualism" deepen it?

In the run-up to the stock market crash of 1929, idealism about American prosperity and the American dream can be considered a strong factor in escalating investments in the stock market, to the extent that "buying on margin" became the norm for stock purchasing.  Buying on margin meant you only had to supply a portion of the stock price -- as low as 10% -- with your own funds and could use borrowed money for the rest.  By the late 1920s, most stock purchases were done that way.  According to one source, 40% of all money borrowed in the United States at that time was being used to buy stocks. This dream of achieving prosperity through risky investing inflated the stock market until that balloon of borrowed funds burst and the market crashed.

America's idea of "rugged individualism" worked against the idea of society pulling together and helping each other through the dark days that followed.  It was a radical change of ideology and approach for the government under President Roosevelt to propose and implement New Deal programs that called for stronger societal aid to those in need.  In an atmosphere of "rugged individualism," individuals are expected to care for themselves and handle their own needs.  But what was needed more (and eventually became a part of American society) was to have people pull together to help everyone have a manageable standard of living.