Our anticipation of, our actual experiences in, and our memory of events are not necessarily the same. In a study by Terence R. Mitchell, Leigh Thompson, Erika Peterson and Randy Cronk it was found that expectations were more positive than actual experiences. It was also found that memories of events were more positive than actual experiences of the event. This was labelled the "Rosy View" phenomenon by the authors.
So, if our expectations are like +2, and our actually experiences are like -1, we will still remember the whole thing as a +1.
Reference
Mitchell, T. R., Thompson, L., Peterson, E., & Cronk, R. (1997). Temporal adjustments in the evaluation of events: The “rosy view”. Journal of experimental social psychology, 33(4), 421-448.