Usability - A summary in just one sentence

This might be quite an unusual question, but its nevertheless related to a software projekt of mine, so I will just go ahead and ask:

Do you know some famous man saying a short catchy phrase about the importance of usability?

In example I bet Steve Jobs has said some remarkable things about usability. However I usually don't listn to his speeches, so I have no idea what he might have said ;-). The whole point of this is, that I have to write a summary for that particular project. A Projekt in which Usability plays a key-Role (As it should in presumably every software projekt), which is why I would like to reference some famous man, stressing the importance of usability ^^.

Moreover I would like to ask you. If you had to sum up the importanc开发者_运维百科e of usability. In just one sentence, what would you say?

Steve Krug said: "Don't Make Me Think" I think this is the essence of usability design.

My summary:

If the user has to wonder how to do their job, your app is broken.