Actually, if you had invested at the market top in 1967 or whenever it was, you would not have had a portfolio with incresed purchasing power until something like 1982. In short for about 15 years, the return was below the inflation rate.
yeah that was the miserable sideways market but she was asking about negative returns and I think you would have eeked out like 2 or 3 % then which of course is so bad you would have been better off in in any of a number of different investments