good analytical approach and experience!

From a Morningstar Analysis of fund holdings and duration:

Of the 59 one-year periods from 1950-2008, 16 resulted in a loss for their particular year. However, if you increase your holding period to five years, only 1 of the 55 overlapping five-year periods resulted in a loss. Moreover, none of the 45 overlapping 15-year periods from 1950-2008 resulted in losses. However, keep in mind that holding stocks for the long term does not ensure a profitable outcome and that investing in stocks always involves risk, including the possibility of losing the entire investment.

Additionally, I will state that the particular period in question may be biased due to the boom that followed WW2 and the potential anomaly of the technology boom that has been relevant for the last 50 years. These factors may not hold true for the next 50 years, which occur under different dynamic circumstances. However, if we consider poor market timing scenarios and the fact that transaction fees and other factors generated from excessive positioning and repositioning (various frantic buying and selling) eat into return yields, a positive trend over the long term from a holding position is a more realistic assumption than a series of educated and subjective selections subject to personal skilll alone.