Summary: we evaluate our memories on the basis of a "peak-end" appraisal. How intense was it (good or bad) at its peak and how did it end? For instance, (and this is the actual example used in the book) two groups of men were rectally probed. Both examinations were equally uncomfortable, but at the end of the second group the doctor left the probe in but unmoving for 20 seconds. Objectively it was worse (the probe being in was uncomfortable), yet afterwards the men in group two reported less dissastisfaction. Why? The peaks were as intense but the end wasn't as bad. This is all based on research by Daniel Kahnemann.