Correct, but I think this is easier said than done sometimes - especially if you've only been investing during a huge bull market. As Mike Tyson once said, "Everybody has a plan until they get punched in the face."
All the more reason to constantly tell people the right thing to do and why and strategies to avoid letting fear and other emotions get the better of them in those situations. We can all be susceptible to such things, but with a little education and discipline can avoid making terrible mistakes like that.