There was a principle of UI design that all UI actions should be discoverable, either with a visible button or a menu item in the menus at the top of the screen (or window on Windows). This is annoying for power users and frequently used actions, so those can also be made available with keyboard shortcuts or right-click actions or what have you, but they must always be optional. This allows power users to be power users without impacting usability for novices.

We've been losing this idea recently, especially in mobile UIs where there's a lot of functionality, not much space to put it in, and no equivalent of the menu bar.