Star Trek: 10 Things You Didn't Know About Jean-Luc Picard
5. Don't Be Afraid To Correct The Captain, Just Make Sure You Bring The Receipts
David Livingston directed Patrick Stewart as Jean-Luc Picard in two episodes of The Next Generation - The Mind's Eye and Power Play. Generally, he found Stewart to be very easy to direct, as the actor had a clear idea of who the captain was, and how to present that.
He did recall one day of shooting, though he was present as a producer this time, not as a director. He was standing off to the side, and he heard Stewart flub a line. Then, to his surprise, the director yelled 'Cut, print.' Livingston then approached both and told him what he had heard.
Stewart disagreed that he had made a mistake, as did the director. Livingston then asked the sound team to play the line back - proving him right. Stewart thanked him, and they reshot the line.
Livingston later joked that telling the captain of the Enterprise that he'd made a mistake was one of the most nerve-wracking things he had ever done, but as his responsibility as a producer overrode all else, he had to speak up. Thankfully the recording team were on the ball!