Even an experienced user often gets lost in a hierarchy of modes and submodes. Menus are bad, because as soon as a user gains the slightest experience, he hates having the screen cluttered up with changing menus. Worst of all are interactive programs that clear the input buffer before accepting a user's command in a new situation. The even slightly experienced user will want to type ahead, often totally ignoring what is on the screen, in order to get the program into a desired state. Keeping up with new programs and improvements in programs has proved impossible so far.
People use only a part of the facilities of our interactive programs.
Many jobs do not involve continuous use of the computer, and it is more important to meet the needs of the casual user than those of the beginner. A person will invest considerable effort in first learning how to use a computer, but if he has to learn all over again after a two-month layoff, he won't put in the effort a second time. Computer use should not be like instrument flying - requiring lessons if you haven't done it for six hours in the last ninety days. The utility of many proposed applications of computers is limited by the work required to put the information in the computer. The prize example is the proposal to use home computers to keep track of items in the pantry and warn the householder when to buy more.