Here's an interesting chart from Bernstein's book..."The Four Pillars of Investing". Two things stick out, that stock returns have been superior compared to long-term and short-term (bills) bonds, and that every so often the stock market crashes. The 1929 and 1973-74 market corrections are very evident on this semi-log scale. The worse case scenario for a new retiree, one who is totally dependant upon a personal portfolio, would be to retire just at the beginning of a large market crash. This is a low probability sequencing of events but it can happen. Therefore, it is preferrable if one's retirement income/spending plan is robust enough and/or flexible enough to weather a possible large stock market crash storm event. A safety factor is is good idea.
To see more detail of the graph (photo) click on the image.