A pretty large chunk of our happiness is genetic.
Several studies done over the past decade estimate that anywhere between 30% and 80% of our happiness is dictated by our genes. One large study of 20,000 pairs of fraternal and identical twins (widely recognized as the easiest way to separate the differences caused by nature and nurture) found that roughly 33% of the variation in life satisfaction is explained by genetic differences.
Other studies suggest that anywhere from 10% to 60% of our happiness comes from our attitude and overall outlook on life.
If you do the math, that means that just a fraction — about 10% of our happiness — comes from external things that happen to us, including changes in our career, relationships, or income.
So while going after that promotion might seem like it'll make you happy, all that stuff only chips away at the tip of the iceberg.
A psychological phenomenon called the "hedonic adaptation" — first coined in the 1970s — states that we all have a base level of happiness that's basically unchangeable — regardless of what happens in our lives.
If we get a job promotion, for example, we'll celebrate and feel good, but those emotions are only temporary, the theory goes.
In the early '90s, British psychologist Michael Eysenck likened this constant starvation for more — and more and more — to a treadmill. Consequently, the "hedonic adaptation" is more commonly known today as the "hedonic treadmill."
"You're running but you're on that treadmill and you're not getting anywhere in terms of happiness," Zukerman says.
Eventually that boost in happiness you get from a job promotion or marriage proposal will abate, and you'll be back to the same baseline level of happiness you were before the exciting change.