It's hard to recognize a thing when you're presented with too much detail. To know that you are seeing a kite, it helps to look for paper, sticks, and string. But if you were to use a microscope, what you'd perceive would not be properties of kites at all, but merely features of particular bits of paper, sticks or string. These might allow you to identify a particular kite but not to recognize any other kite. Past a certain level of detail, the more one sees, the less one can tell what one is seeing! The same applies to memories; they should weaken their attachments at lower levels of detail.
Lower Band: Beyond a certain level of detail, increasingly complete memories of previous situations are increasingly difficult to match to new situations.
To explain why K-lines need an upper-level fringe, let's return to that example in which our child originally learned how to build a tower — but now desires to build a house. Here, we could have another kind of difficulty if we remembered too much about our previous goals!
Upper Band: Memories that arouse agents at too high a level would tend to provide us with goals that are not appropriate to the present situation.
To see why our K-line memories should weaken their attachments above a certain level of detail, consider this most extreme form. Suppose some memory were so complete that it made you relive, in every detail, some perfect moment of your past. That would erase your present you — and you'd forget what you had asked your memory to do!
Both fringing effects serve to make our memories more relevant to our present purposes. The central level-band helps us find general resemblances between remembered events and present circumstances. The lower fringe supplies additional details but does not force them upon us. We use them only by default when actual details are not supplied. Similarly, the upper fringe recalls to mind some memories of previous goals, but again, we're not forced to use them except by default, when present circumstances do not impose more compelling goals. Seen this way, we can think of the lower fringe as concerned with the structures of things, and we can think of the upper fringe as involved with the functions of things. The lower levels represent objective details of reality; the upper levels represent our subjective concerns with goals and intentions.
How could the fringes of the same K-line lie in two such different realms? Because in order to think, we need intimate connections between things and goals — between structures and their functions. What use would thinking be at all, unless we could relate each thing's details to our plans and intentions? Consider how often the English language employs the selfsame words for things and for their purposes. What tools would you use, when building your house, to saw and clamp and glue your wood? That's obvious: you'd use a saw and a clamp and some glue! Behold the wondrous force of those meanings: no sooner do we hear the noun form of a word than our agents strain to perform the acts that correspond to it as a verb. This phenomenon of connecting means with ends is not confined to language — we'll see many other instances of it in other kinds of agencies — but language may allow such linking with the least constraint.