Chapter #25. Split Menu Items Down into Subsections, so Users Don't Have to Remember Large Lists
Humans are better at some things than others. We're really good, for example, at drawing a pretty picture of a flower, but we're not so good at instantly recalling the precise genus of that flower and its scientific name. Computers are better at that kind of thing.
The rule of thumb for the number of items that a person can reasonably remember and juggle in a list, is "seve, plus or minus two." (The Magical Number Seven, Plus or Minus Two: Some Limits on our Capacity for Processing Information, George A. Miller (1956) (https://www.ncbi.nlm.nih.gov/pubmed/13310704)). This research has been around since the 1950s and has been revised and re-evaluated many times over the years. I'll spare you the psychological study details, but the short version is: it's pretty much true.
The "magic number seven" will change depending on the items being recalled, the context, and environmental factors like state...