It’s just started to rain and she had to act quickly!

The umbrella should’ve been an invisible interface, since good usability is designed not to be something intentionally noticed as the user try to accomplish his goal. In this case, her goal was to protect herself from the rain, not to simply open the umbrella itself (the task).

But then she became ‘aware’ of the umbrella interface just because it didn’t work fine. (Poor usability, on the other hand, is always perceived by the user).