"I can picture exactly how it'll feel"

Part of what makes the next thing so convincing is the clarity of the preview. You can see the kitchen. You can see yourself at the table in the new job, you can see the town, the walk to the shops, the evenings. The preview is detailed and it comes with a feeling attached, and it seems reasonable to treat a preview that clear as a reliable forecast. If you can see it that well, you must know how it'll feel.

Timothy Wilson and Daniel Gilbert spent years studying how well people predict their own future feelings, and their summary of the field in 2005 has a name for the main error. They call it the impact bias. People overestimate both how strong their emotional reaction to a future event will be and how long it will last. One cause is what they call focalism, which is the same error as chapter 4 in a different coat. When you picture the new life you picture the new thing, and you leave out everything else that will also be going on, the work, the weather, the argument about whose turn it is, the tiredness on a Thursday. The preview is clear because it's been emptied of everything but the feature.

The other cause they name is stranger. People fail to anticipate how quickly they'll make sense of what happens to them. Whatever arrives, good or bad, the mind gets to work on it, explains it, files it, makes it ordinary. That process is fast and it's mostly invisible, and because it's invisible it never makes it into the forecast. You picture the kitchen as it will look on the first morning. You don't picture the morning six months later when it's just the kitchen, because from here you can't feel the process that will make it so.

An earlier paper by Gilbert and colleagues found the same thing running the other way. In six studies, people were asked to predict how long they'd feel bad after events ranging from a relationship ending to being turned down for a job, and they consistently predicted their bad feelings would last longer than they did. The authors called the machinery that shortens the bad feelings a psychological immune system, and the error of leaving it out of the forecast immune neglect. It matters here because the same machinery works on the good feelings. The system that makes a rejection bearable in a month is the system that makes the new kitchen ordinary in six.

So the clarity of the preview is not evidence about the future. It's evidence about what you've left out. A forecast that includes the other things going on, and includes the mind's habit of making the new thing ordinary, is blurrier and more accurate, and it's the one chapter 18 asks you to make. What you can picture exactly is the first morning. Nobody can picture the two hundredth, and the two hundredth is where you'll be living.