Contrast that with the actual experience of the trip and you may find that the anticipation was better than the trip. In fact, Terence Mitchell (1997) conducted research on just this situation. He studied people who were taking either a trip to Europe, a short trip over the USA Thanksgiving holiday weekend, or a 3-week bicycle tour of California.
Before the event people looked forward to the trip with positive emotions, but during the trip their ratings of the trip were not that positive. The little disappointments that always occur while traveling colored their emotional landscape to the point where they felt less positive about the trip in general. Interestingly, a few days after the trip, the memories became rosy again.