Holy cow, I wrote a book!
Sometimes psychic debugging consists merely of seeing the bigger picture.
On one of our internal bug-reporting mailing lists, someone asked,
"How come when I do XYZ, my CPU usage goes to 50%?"
My psychic answer: "Because you have two processors."
The response was genuine surprise and amazement.
How did I know they had two processors?
If they had only one processor, the CPU usage would be 100%.
This seems unhelpful on its face, but it actually does help
diagnose the problem,
because now they can
search the bug database for bugs in the XYZ
feature tagged "100% CPU" to see if any of those apply
to their situation.
(And in this case, it turns out that one did.)