I was working with a new office in Salt Lake City.
My job was to get them up and running on the software.
And I worked with their admin, gave them the test TNSNames.ora file as we were working in Oracle.
And the day came to go live, I sent the production TNSNames settings.
The admin called my boss immediately, said users were complaining, runtime was too slow.
We had a conference call, was my code causing it?
I didn't think so as it ran fine in Tampa.
I went back to my desk and thought about it.
Then went back to my boss, said I think they're pointing to the test database.
We call the admin, he said no way,that wasn't the problem.
After we hung up, my boss said to me,"Go shut the test / dev server".
So a few minutes later I shut the oracle database.
And two minutes later, the admin called asking what happened to his database.
Problem solved, he was pointing to test.
That's called troubleshooting in a black box!