Nine Eleven lemonade

Clyde : Alan, what does the phrase every cloud has a silver lining mean? 

Alan : It means every bad thing that happens also has a positive side effect. 

Clyde: What about the Nine Eleven Terrorist attacks? Does that have a silver lining? 

Alan :  Well, yes it does. 

Alan :  The nine Eleven Terrorist attacks makes it easier to remember how many days each month has on the Gregorian Calendar.

Month number nine and eleven both has 30 days, there was four planes hijacked, the 4th month also has 30 days. The sixth month has 30 days  but they cut corners with the hexagon and built it has a Pentagon instead, my jokes aren't funny. 

Four, Six, Nine, Eleven ( April, June, September, November) has 30 days, the rest has 31 except for February, it is "2" short with only 28 days or 29 days on a leap year. February is the second month of the year.