My favorite director comments, and we've all heard them, "If they're paying attention to that, they're watching the wrong thing", "No one will notice", and "It doesn't matter".
During a recent production, I noticed that a principal character was missing a prop. While I was pointing out the error to props, the director overheard and said "No one will notice" ( the character was in the background of a particular shot). The prop was integral to the character and even though he was in the background, I could see on the monitor that the prop was missing. I felt it would be a huge continuity error, so I replied "When your fans watch this movie again and again because it's a cult classic, they'll notice the error." The director smiled and took the time to dress the character with his prop. One win for me.
Of course, there have been arguments I have lost. For example, a director decided that it was OK to change an actresses hairstyle from one scene to the next, his rational was that she could have changed it during the car ride over. Wish we could explain those arguments to the audience.
But on the bright side, don't you love it when you work with brilliant directors, cinematographers and actors! Don't you love it when the producers come to you for answers and you have them! Don't you love it when there are Heath Bars at craft service (I do.)