The problem is that the more Sevens fill up their minds anticipating the fun they will have in the future, the less they are in touch with whatever experience they are having in the present. Consequently, the experience they are currently having cannot really affect them, cannot really satisfy them. This is like the person who has always wanted to see the pyramids in Egypt, and after much anticipation, finally embarks on a trip to see them. However, on arriving at the pyramids, the person is anticipating an exciting dinner in Cairo that night, or perhaps thinking about showing friends back home their pictures of the trip, and so "misses" seeing the pyramids. The person’s attention is elsewhere, no on the experience that they are having. Naturally, this decreases the enjoyment of the experience, leaving the Seven hungry for more.
As enjoyment decreases, average Sevens feel anxious and insecure, leading them to overdo their activities all the more.