She argues that most people fall into two categories. There are those who worry a lot and are therefore motivated by the need to avoid bad things happening to them; behaviour which psychologists call "harm avoidance".
Then there are the more optimistic, who are primarily motivated by the desire for positive outcomes in the future.
In her research, Dr Tamir argues that the neurotic or worriers among us choose to worry because it helps us improve our performance in life. In a series of elegant experiments, she demonstrates that worrying tends to motivate the neurotic to perform. So, for example, they work hard for an exam because they are terrified of failure, whereas the non-neurotic study hard because they want to enjoy the fruits of success.
These results have key implications for motivation. If you tend to worry a lot, what might best motivate you to tackle a difficult task is a fear of a bad consequence. Another way of thinking about this is to examine a classic motivational scenario for many people: they have a significant event coming up, such as a wedding, and want to lose weight for the big day. The neurotic want to get thinner because they are worried about looking fat in the wedding videos, while the non-neurotic want to lose weight because they are anticipating the guests' admiring glances.
At first glance, both groups appear to be motivated for the same event and for the same reason. But one group is being driven by terror of an awful outcome while the other is focused on anticipating good things. Losing weight and avoiding appearing bloated on the wedding videos will make the neurotic happy, but for a different reason: relief at having avoided a bad outcome.
So while we may all seek happiness, we seek it for different reasons. The key is to find out what motivates us as individuals. Viktor Frankl, a famous psychiatrist who survived a Nazi concentration camp, put it this way: "A human being is not one in pursuit of happiness, but rather in search of a reason to be happy."
Dr Raj Persaud is consultant psychiatrist at the Maudsley Hospital in south London and Gresham professor for public understanding of psychiatry. His latest book is The Motivated Mind (Bantam Press). Email: email@example.com