Gilbert and Wilson offer an engaging essay in the Philisophical Transactions of the Royal Society B (PDF here) titled: "Why the brain talks to itself: sources of error in emotional prediction." In trying to plan futures that involve more pleasure than pain, we perform mental simulations (previews) of future events, which produce affective reactions (premotions), which are then used as a basis for forecasts (predictions) about the future event’s emotional consequences. Their review summarizes several main sources of systematic errors of these predictions.
Previews have several problems of dissimilar content:
1. They provide a poor basis for prediction because they tend to be based on memories that are not representative of the future events that those previews were meant to simulate.Previews also have problems of dissimilar context:
2. They tend to omit features that are incidental to the event but that nonetheless may have a significant impact on our emotional reactions to it.
3. They tend to emphasize the early occurring moments of the event in which emotions are likely to be the most intense.
4. They include comparisons that views do not. (Imaginary chips are readily compared to imaginary sardines, but real chips are not.)
...accurate predictions also require that the context in which previewing occurs be similar to the context in which viewing occurs, and as it turns out, this is not always the case either. Why do contexts matter? Premotions are not just reactions to previews; they are reactions to previews and to the context in which those previews are generated. That is why we feel happier when we preview chocolate cake while we are lying on a comfortable couch than on a bed of nails, or when we are hungry rather than sated.