Survey says only about half of all lottery winners are happy three years after their windfall. And there are plenty of examples of winners whose lives have been ruined by their winnings.

A few years ago, CNN introduced us to four big winners who either died soon after winning, or eventually regretted cashing in their tickets.

We've always heard that money can't buy happiness, but why?

In the video below, Psychologist Auduan Tartt tells CNN that when you have money, you spend money and quickly grow accustomed to spending money.

"You actually have to spend more money to get the same level of happiness."