What gives? Behavior experts have a couple theories. One is simply that we humans just tend to get used to stuff — the good and the bad. The psychological concept is called “happiness adaptation,” and Michael Norton, associate professor at Harvard Business School, co-authored a 2007 paper that sought to uncover why hitting major life goals — including the dreamlike goal of winning the lottery and the more down-to-earth goal of getting married — don’t end up making us as happy as we expect them to.

“The idea of adaptation seems like a negative thing — it’s a shame that we have to get used to the good things in our life, from lottery winnings to ice cream. But adaptation also helps us when bad things happen to us, making the impact of losing our job or getting divorced less painful over time,” explains Norton, who is also the coauthor of the forthcoming book, “Happy Money: The Science of Smarter Spending.”

He continues, “Big positive and negative events can have a lasting impact on our happiness, but this impact tends to decrease over time. In some sense, because people have so many facets of their life – from their job to their friends to their family to their hobbies – the impact of a change in any one of those facets is less extreme than we think, because many of the other things in our lives stay the same. (We win the lottery but we are still stuck with our same siblings, for example.) As a result of this, people tend to adapt to life events and end up closer to where they were than they think they’d be.”