When it comes to investing money in the stock market, investors should create a balanced portfolio and then actively rebalance their portfolio as the market goes up and down, according to Professor Michael Stutzer of the CU-Boulder Leeds School of Business. It sounds simple enough, Stutzer said, but many investors don't do it. Instead they jump in and out of the market or just let their money ride, and when the market goes down many are left behind the curve holding too many stocks or not enough bonds.