This is a well-trod point, but one that's always good to be reminded of. A similar argument is made in The Design of Everyday Things - if your interface needs a

This is a well-trod point, but one that's always good to be reminded of. A similar argument is made in The Design of Everyday Things - if your interface needs an instruction manual, even if it's only one word (for instance the word "pull" on a door) then the interface is not doing its job. I'd highly recommend DOET for anyone interested in this sort of thing.