Understanding and updating beliefs on deeply engrained topics can take enormous efforts, but sometimes it can be so hard that the listener cannot even in principle accept the new reality. The listener is simply not ready, he lacks a vast background of reasoning leading to the new understanding.
What fact that you know is true but most people aren't ready to accept it?
By "you know is true" I really mean "you are very confident to be true".
Feel free to use a dummy account.
I had a personal experience that strongly suggests that this is at least partially true.
I had a mountaineering trip in a remote location that went off the rails pretty badly — it was turning into a classical "how someone dies in the woods" story. There was a road closure some miles ahead of where I was supposed to drive, I hiked an extra 8 miles in, missed the correct trail, tried to take a shortcut, etc etc - it got ugly.
I felt an almost complete lack of distress or self-pity the entire time. I was just very focused methodically on orienting around my maps and GPS and getting through the next point.
I was surprised at how little negative internal discourse or negative emotions I felt. So, n=1 here, but it was very informative for me.