Ran across a very interesting article, in the NYTimes magazine, about a line of inquiry into happiness, behavior and decisions.
The major psychological thrust was that we're not very good at predicting how we will feel after an anticipated event. For example, we tend to underestimate how quickly we will adapt to that shiny new gadget (say, an LCD HDTV with native 1080p resolution). In the other direction, we also tend to underestimate how quickly we will overcome adversity (e.g., a car accident).
The authors term this "impact bias"; impact because the subject is the duration and intensity of the feeling, bias because we tend to underestimate it.
The major economic thrust of the research is that we're not very good at predicting how we will behave during periods of anxiety, distress, etc... The proponents broadly term these "hot states". For example, mountain climbers that find themselves stuck w/o shelter in frigid temperatures may, under calmer circumstances, swear that they'll stop climbing the next time they're more than X feet away from shelter/food/camp only to find themselves breaking this promise the next time they're in a similar circumstance. Climbing up a mountain will the sun is setting is the hot state; calm circumstances are the "cool state" and the variation in anticipated behavior (what we think we will do in a hot state) is often wide.
Very interesting research. Another consideration that the researchers (Daniel Gilbert of Harvard, Psychology dept, George Loewenstein of Carnegie-Mellon, Economics dept, and a few others) and find is that the brain's adaptability doesn't seem to kick in until the intensity of the event is pretty high (either strongly positive or strongly negative). So we underestimate how quickly we'll get over a car accident but overestimate how annoying a squeaky door or broken bed spring will be.
In one experiment the participants are allowed to choose from a set of pictures. One group is told that their choices are final. The other is told that they can exchange the photos a few weeks later. The researchers find that the people who couldn't change photos were happier than those who could! I believe they interpret this as an example of underestimate just how bothersome "buyer's remorse" or "missed opportunities" will feel.