What could explain the blinding speed of sight? Expectations! Something like stereotypes could provide mechanisms for efficiency. "The moment you sense the presence of a person, a whole world of assumptions are aroused that are usually true about people in general. At the same time, certain superficial cues remind you of particular people you've already met. Unconsciously, then, you will assume that this stranger must also resemble them, not only in appearance but in other traits as well." For Minsky, these expectations are provided by frames.
NB: Relating this to material in Chapter 23, comparison is at the base of this too. As well, assuming that few differences exist between agencies is here too. Presumably, to break away from a frame for a particular person, difference detection would have to kick in. One wonders, then, if you could represent people as a stereotypical frame, duplicated, with specific differences made explicit...