Thank you Mr. Ritholtz.
I have a stock that since acquisition has hit  a high of 25% and now is minus 52%. So in my case this is a very timely article.

First, I appreciate # 1; specifically "Experience teaches us that most of the news is old, and is already reflected in stock prices and is not a credible reason to sell."
I did not know nor consider this fact. 
-Also- 
Second, I appreciate # 5; specifically " Finally, there are the issues not just of the probabilities, but the costs and taxes."
In my case my stocks are in a registered tax-free portfolio so although 'taxes' are not an issue, the cost/loss is.
-Finally-
Third, some individuals advisors suggest sell every stock that drops down 20%
from your purchase price and then wait until it hits 'bottom' and buy in again to recoup your losses as long as the stock is below it's 'target price'.
Great when do I know when it hits 'rock bottom' and how do I know succinctly what it's target price is?
Please now an article what about buying.