Why does the computer work for the tech but not for me?

When I go to peoples houses to repair their computers, I always ask the customer to demonstrate the problem they're having.
Naturally, when I sit at the computer and turn it on, it works normally. Isnt that just they way things work for mechanics and repairmen? Of course it is; just like when you take your car to be fixed.

When this happens, I try to give the customer an explanation of why this may be happening.
"It's a peculiar form of electromagnetic radiation," I say. I call it the 'tech-field radius;' its the distance a broken object must be from a repairman who is intent on repairing it.

This description works for any repairman or mechanic.

One day I was at a customers house, an older gentleman, and he asked the question I had heard many times before, "Why...?"
As I was in the middle of my somewhat complicated technical-sounding explanation of EMF's and radiations and such, he interrupted me and said, with a very definite tone, "Nonsense! It's pixie dust!"

And that's now what I tell people. It just makes more sense.