If you follow a Dogs of the Dow investment strategy, you buy the ten highest-yielding stocks in the Dow Jones Industrial Average (DJIA) on the first of the year and hold them for a year.
According to this theory, the dogs will, over the year, produce a total return, or combination of dividends plus price appreciation, that's higher than the return on the DJIA as a whole. The increasing price is the result of demand for the high-yielding stock.
On the anniversary of your purchase, the stocks are no longer dogs because their higher prices reduce their current yield even if the dividend remains the same. So you sell them and buy the next batch of dogs.