Debt, geopolitics, unexpected world events and a widespread sense of general happiness: these are the things that worry private equity billionaire David Rubenstein the most.

The co-founder of global private equity firm Carlyle Group detailed his concerns while speaking at the World Economic Forum in Davos, during a panel on Tuesday entitled "The Next Financial Crisis."

"Right now, the biggest concern I have is that most people think there is no problem of a likely recession this year or even maybe early next year. Generally when people are very happy and confident, something wrong happens," Rubenstein cautioned at the Bloomberg-moderated panel.

"I am nervous that the conventional wisdom is that we have no recession problems around the world, that everybody's doing quite well ... The conventional wisdom is usually wrong, and it might be in this case."

The American businessman and philanthropist went on to explain why debt and geopolitics are further sources of concern.