I used to work as a teaching assistant for an undergraduate computer networking course at UBC. As part of the course, we would usually ask the students to write a simple line editor, in order to practice their IO programming skills. This was an assignment designed by a professor in the early 1980s, when being able to work ed was considered a basic computer skill.

Fast forward to 1999, and I can say that roughly 80% of students in the class didn't know what ed was. Before being able to get started on the assignment, we would have to provide them with additional material explaining how to use a line editor and why you need one. The majority of students just grew up using Emacs, VI, Notepad or whatever visual editor they had on their computer, so they had no idea of what we were asking them to build.