ExxonMobil (XOM -3.48%) was recently downgraded by Morgan Stanley. But with a company like Exxon that has a long history of a rock-solid balance sheet, excellent reserve replacement, and the ability to return enormous amounts of money to shareholders, what is holding back the world's largest oil company? In this video, Motley Fool energy analysts Joel South and Taylor Muckerman discuss Exxon's 2009 acquisition of XTO Energy, and tell investors how overpaying in an acquisition continues to hurt investors.