That mitigates some of the damage done by unclear icons. You push the button... oops, that didn't do what I thought it did. Well, now I know, and the Undo button fixed it, so we're all good.

That's not perfect, but it does let regular users and power users coexist without separate modes. The former become the latter smoothly, without having to decide one day "OK, I don't need the screen real estate for labels, so turn them off".

In this case the Undo mode is also very imperfect: GMail has it inconsistently, and it's modal. It exists only in a toast, and not as a general Undo button in one consistent place. It's not a full stack, another thing that Raskin strongly encouraged. That indicates a significant re-think is necessary, not just tweaking the labels.

Anyway... really good book. It's not just UI tips and tricks, but a new way to think about what a UI is.