"There is a limit to the number of items we can keep in
short-term memory - 7 plus or minus 2.
"While not applicable to basic lists - where the reader doesn't
simultaneously need to be aware of every item in the list - it is a
powerful heuristic when applied to, for example, a software
architecture layer. In this case a person trying to understand the
architecture would benefit from awareness of all parts of the
architecture at the level being studied, and in doing so finds the
architecture more easily discoverable and transparent than if the
layer were more finely partitioned."