I just had the most embarrassing moment in programming... I am writing an administration / client / invoice webapp and I was testing an export function that worked locally, because everything that was being exported was inside the folder.

So I exported the files in test production, but some invoices didn't exist. So when they don't exist, the system creates a new invoice.

Because I was running on the test production (with client data) the system emailed the created invoices to the clients.. now I have to contact some clients and tell them the invoices were sent accidentally.