I believe the Dow fell today because of one or maybe two reasons. One is that with the majority of stocks, bonds, and other investments now being purchased using the Internet, investors just have a hard time getting excited about Cyber Monday, a day when the rest of America buys items over the Internet. The second is perhaps that a good number of Internet traders were busy buying gifts for family and friends instead of stocks and bonds, and the lack of market participants caused equity prices to fall. (Fun Foolish thinking.)

Whatever the reason was today, the Dow Jones Industrial Average (DJINDICES:^DJI) closed down 42 points and now sits at 12,967. Today, only eight of the Dow's 30 components ended the trading session in the green. With 22 stocks in the red, we can blame the Dow's fall on a number of different companies, which I have done today. This afternoon I discussed why AT&T (NYSE:T), Verizon (NYSE:VZ), Bank of America (NYSE:BAC), and JPMorgan Chase (NYSE:JPM) all moved lower. Read about what caused those four companies to fall into the red by clicking here, or stick around to learn why Travelers (NYSE: TRV), McDonald's (NYSE:MCD)and UnitedHealth Group (NYSE: UNH) also moved lower.

So why did they fall?
The Dow's loan insurance company, Travelers, fell by 0.58% after AIR Worldwide, a catastrophe modeling company, increased its estimates of the damage caused by Hurricane Sandy. Previous estimates forecasted losses from a low of $7 billion to a high of $15 billion. The previous numbers were announced the day after the storm. The revised numbers, announced today, now put the low end at $16 billion and the high at $22 billion of damage. Air Worldwide said the storm surge caused more damage than the company previously predicted and that accounted for most of the change.  

Shareholders of McDonald's also lost today, as the stock slid 0.93% lower. Lazard Capital downgraded the company this morning because of tough competition and concerns over recent management changes. Other fast-food restaurant chains have increased pressure on McDonald's with new menu items and refreshed advertising campaigns in recent months. Lazard also called the departure of Jan Fields an "abrupt firing" and said the move raises concerns about the company's direction moving forward. McDonald's shares are now rated "neutral" from Lazard, while the previous rating was a buy.  

UnitedHealth announced this morning that 2013 earnings are likely to fall somewhere in the range of $5.25 to $5.50 per share. The company's guidance was below the $5.60 per share Wall Street had previously estimated. Back in October, the company made comments indicating that because of a weak economy and deficit reduction efforts by the U.S. government, analysts' estimates for 2013 were too high. Today's announcement put hard numbers behind where management believes earnings will fall over the next year and reins in investors' expectations. Shares of UnitedHealth lost 0.72% today. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.