Suddenly, our offshore colleagues could not access the database. We scrambled to find a solution, and it soon transpired that the central security function had rolled out out a security policy upgrade the night before. Unfortunately, our offshore colleagues were connected to the network in an uncommon way, so the new security policy cut them off.
You don’t know what will happen when you change a system. Enterprise IT landscapes have reached a complexity where no amount testing can cover all scenarios. All you can do is to make sure that you test, you are prepared for any problems that might arise, and can recover.