And it's not just keyboard modifiers -- in middle school I remember having to explain double clicking. People eventually got used to it, then the web got popular, and I had to explain to users not to double click on web links but do click on desktop links. Even in this century I still occasionally see people using double click to navigate the web.

Could be argued that that was a mistake in the original specs for the Web. At the time, as I recall it, "double-click for action" was already a pretty well-entrenched standard on multiple platforms.