US News:
Study: Happiness is a U and Middle Age is Depressing
22 August 2017
A new study suggests midlife "psychological low" points are a global phenomenon
Why people consistently report being near their most unhappy around the same age – across countries, incomes and demographics – has generated much debate. Hannes Schwandt, an assistant professor of economics at the University of Zurich, theorized back in 2013 that "the U-shape is caused by unmet expectations that are felt painfully in midlife."