We are creatures of memory and anticipation, continually storing the memories of our experiences in the Hippocampus for later access. This ongoing cycle of psychological impressions (called "Samskaras" in Buddhism) is the very nature of the human mind, and believed to be the root of all suffering. Unless we're aware of this self-fulfilling prophecy, the older we get, the less new experiences we have. This is nature's way of conserving energy; if you have had this experience before, your nervous system doesn't have to figure out a new way to react to it.