Earlier quoted context omitted.
Can't completely agree there. Contextual menus by right-click (or ctrl-click) have been core since OS X came out in 2000. (I would distinguish between "core" meaning extremely useful and effective, as opposed to "essential" meaning the only possible way to accomplish a task. Right click is still not "essential," just very useful.) And back in the pre OS X days, tons of functionality was "hidden" with the option key.…
Lots of magical things are still hidden behind modifier keys. Option-click the wifi icon: special diagnostics info Option-click the bluetooth icon: diagnostics info Shift-Option-click the bluetooth icon: debug menu Hold option while resizing a window: resize from both sides at once (see gif: https://twitter.com/dceddia/status/859518600931143680 )
The option-resize window trick is crucial when you come across a monitor/video card bug that doesn't let you touch the edge of the window that you need to drag in order to bring the window on-screen. Just option-drag the opposite edge as a workaround.