Ignore what isn't understood
Never under estimate the user's ability to just have blind spots about what is happening on screen.
I once sat through a user demonstrating a problem they were having when booting their computer. They insisted it there was no error message, and it was just freezing. I ended up sitting next to them as the computer booted. In course of booting an error dialog appeared, but they clicked on it before I had time to read it.
"What was that?" I asked.
"What was what?" they replied.
"That error message you clicked."
"I didn't click anything."
"I just saw you. Let's reboot again. Do not click on anything."
Turns out that their computer had been warning of an impending full C: drive for months, but they didn't understand what it was saying, so had just been ignoring it. They had got in the habit of just clicking OK on the warning so often, they'd stopped even registering they were doing it. I practically had to grab the mouse off them to stop them.