Don’t Make Me Think, Revisited a common Sense Approach to Web Usability Steve Krug

Don’t hide your affordances under a bushel
Affordances are visual clues in an object’s design that suggest how we can
use it. (I mentioned them back in 
Chapter 3
. Remember the doorknobs and
the book by Don Norman? He popularized the term in the first edition of 
The
Design of Everyday Things
in 1988 and the design world quickly adopted
it.
4
)
4
 
Unfortunately, the way they used it wasn’t exactly what he intended. He’s clarified it in the new
edition of
Everyday Things 
by proposing to call the clues “signifiers” instead, but it may be too
late to put that genie back in the bottle. With apologies to Don, I’m going to keep calling them
affordances here because (a) it’s still the prevailing usage, and (b) it makes my head hurt too
much otherwise.
Affordances are the meat and potatoes of a visual user interface. For
instance, the three-dimensional style of some buttons makes it clear they’re
meant to be clicked. The same as with the scent of information for links, the
clearer the visual cues, the more unambiguous the signal.
In the same way, a rectangular box with a border around it suggests that you
can click in it and type something. If you had an editable text box without a
border, the user could still click on it and type in it if he knew it was there.
But it’s the affordance—the border—that makes its function clear.

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For affordances to work, they need to be noticeable, and some characteristics
of mobile devices have made them less noticeable or, worse, invisible. And
by definition, affordances are the 
last
thing you should hide.
This is not to say that all affordances need to hit you in the face. They just
have to be visible enough that people can notice the ones they need to get
their tasks done.