Not necessarily, it also comes from taking your users seriously before you even know what they were saying.
Consider: If you trust the people on your forum to be sensible, and one day one of your users writes:
"I have realised something which is dangerous to know. Here it is: …"
then the sensible choice is to (1) stop reading immediately, don't even find out what's after the ellipsis, (2) delete/hide/otherwise remove their message, and (3) put in a general statement of "don't write things that you think are dangerous for people to know".
Consider: If you trust the people on your forum to be sensible, and one day one of your users writes:
then the sensible choice is to (1) stop reading immediately, don't even find out what's after the ellipsis, (2) delete/hide/otherwise remove their message, and (3) put in a general statement of "don't write things that you think are dangerous for people to know".