This article by designer Jeff Davidson is an informative reminder of the well-known observation that human working memory has a capacity of 7 items (give or take 1 or 2).
This observation, originally posited by cognitive psychologist George A. Miller in his paper The Magical Number Seven, Plus or Minus Two is a crucial guideline for designing user interfaces.
If a user interface contains more than that number of different chunks of information it’ll appear cluttered and overloaded to the user, who will not be able to make heads or tails of it at first glance. Conversely, if a user interface is composed of less components it’ll be easier to grasp and look focused and clean.