In an organization built around perfection, you need to push people to say, "Bad news, I made a mistake." Only by surfacing mistakes can the organization stamp them out.
In an organization built around exploration, on the other hand, people need to say, "Good news, I made a mistake." Only by seeking things that don't work will the group end up exploring.
In both situations, people don't want to speak up, because we've been taught that mistakes should be hidden. In both situations, though, hiding them is the very worst option.