He may have been completely mistaken about his manuscript.

Unless I'm completely mistaken, and what we're dealing with here is a poltergeist.

"They've been completely mistaken, and we think they're wrong this time too."

It turns out that I'm completely mistaken: people do want to hear about other people's problems, more and more so.

Those who believe that the Government wants war are completely mistaken.

Those who say that it would have been better not to confront the criminals are completely mistaken.

This fresh development has shown me that I was completely mistaken.

I told her that she was completely mistaken.

Clearly he was completely mistaken about his position.

Clearly, that view would not be completely mistaken.