If prices are as likely to increase as decrease why do investors earn a positive return from the market on average?

Over the long haul, there is an expected upward drift in stock prices based on their fair

expected rates of return. The fair expected return over any single day is very small (e.g.,

12% per year is only about 0.03% per day), so that on any day the price is virtually

equally likely to rise or fall. However, over longer periods, the small expected daily

returns accumulate, and upward moves are indeed more likely than downward ones.