12 Lost Years For S&P 500
Another way of looking at it is going back to the first time the S&P 500 rose above 800. That is relevant because it illustrates how long a "buy and hold" strategy has been a losing strategy, something which in turn illustrates the depth of the slump.
While people who have held stock during that time have received dividends, the opportunity cost in the form of interest bearing assets (particularly those of a similar risk level) is in fact higher than dividend payments, meaning that simply looking at index levels if anything underestimates how bad the "buy and hold strategy" has been.
If you then look at the historical data, it turns out that the first time the S&P 500 was trading above 800 was in February 13, 1997, slightly more than 12 years ago.