They say that money can't buy happiness, but that may not be entirely true. Research conducted by Harvard Business School professor Michael Norton and Ph.D. student Grant Donnelly found that self-made millionaires worth over $8 million are happier than less wealthy millionaires, and that millionaires who earned their wealth were happier than those who didn't.

Norton and Donnelly worked with Tianyi Zheng from the University of Mannheim and Emily Haisley, behavioral finance director at BlackRock to survey over 4,000 millionaires around the world in order to better understand the ways wealth impacts happiness.