Expect Users to Remember No More than Three Things

This is a result of designing human interfaces back in the all input came from a keyboard days. I discovered people could be expected to reliably remember three key stokes: <ENTER> to accept the default and continues, <ESC> to quit and go back, and <F1> [later <F10> or <F12>] for help. Every other key stroke had be explained or there would be user problems. This made sense to me as I remembered how primitive counting tended to be 1, 2, 3 many.