Buying the dip doesn't mean you expect to hit the exact bottom of the market. As you start buying the dip, you know that it may drop further. nobody can time the exact bottom. The point is that you are getting the stock at a good value and it will recover over time.
Suppose a stock is at 30 on monday and drops to 20 on tuesday so you buy some and on Thrusday it falls to 15, so you buy some more, then it falls to 12.You have your shares at say an average of 18 so on paper you lost 6 per share...