"The stock market (equity market ) has tended to produce statistically positive returns over a long time frame and has therefore been the most reliable source of long term returns amongst many asset classes."
Why would we care ?
Because, as a working citizen ( of the U.S. / North American continent ), you are responsible for saving and growing money for your retirement.
These accumulated savings can be placed in different locations in order to produce some expected return and these savings will be at the mercy of inflation. Inflation is the rising prices / cost of goods and services that we, as consumers, use. In modern life, we can't easily get around the use of these goods and services. Has the cost of going to the dentist, paying for...