By Daniel Jordan Photography @Shutterstock

OK, this stock market is top heavy. Remember, you buy the stock market when you buy a 500 index. But do you know how that index works? Look at the S&P 500 for example. Sure, it’s 500 stocks, but about a third of the index is dependent on five companies. Why? Because it’s a market cap weighted index meaning the size of a company, its market cap (price times shares outstanding) dictates its influence.

โ€œRemember when a trillion dollars was a lot of money?โ€ asks Spencer Jakab in The Wall Street Journalโ€™s Heard on the Street feature, โ€œGigantic Stocks Are a Reason to Worry.โ€ Five companies have reached that level recently. And look at Apple. Its market cap is approaching $3 trillion. What does this mean? โ€œThe precedents arenโ€™t encouraging,โ€ explains Jakab and he continues why, here:

One obยญviยญous reaยญson is that even pasยญsive inยญvestors are inยญcreasยญingly betยญting on just a handยญful of stocks vulยญnerยญaยญble to a dud prodยญuct or regยญuยญlaยญtory setยญback. Thinkยญing of it in terms of buyยญing an enยญtire busiยญness is helpยญful: Would you rather own the iPhone maker or all of McยญDonยญaldโ€™s, Walยญmart, AT&T, Philip Morยญris, Berkยญshire Hathยญaway, Procยญter & Gamยญble, JPยญMorยญgan Chase, Starยญbucks, Boeยญing, Deere and Amerยญiยญcan Exยญpress comยญbined? A lot would have to go wrong all at once to torยญpedo that diยญverยญsiยญfied group of blue-chip stocks.

Action Line: This is a top-heavy market where you need to ask yourself how many iPhones can Apple really sell? Invest every dollar like itโ€™s your last. And invest in terms of thinking about having that dollar buying a business.