Giving too much docs to a customer
The last two days I had to fiddle around in DBs and logfiles to create and/or confirm statistical numbers a customer sent us from our system.
The problem was that according to his calculations we were loosing nearly one percent of all billing data.
He collected the numbers by counting through our logfiles and internal DB tables with grep and custom SQL selects.
Of course he got his numbers wrong.
But it was on our side to prove, that he was wrong and what exactly our numbers and his numbers contained.
Of course again I got it wrong too the first time, because our specialists for these areas are on vacation and I had to dig in into the DB structure without exact knowledge of different columns meanings.
Well now, after two days and with the help of another DB specialist we could send the customer a (hopefully well enough documented) explaination of the numbers and how we acquired them.
Never let a customer dig around in your internal structures!