You may have heard of some Gmail problems some days ago that prevented some (MANY!) users to have any access to Gmail
Here is the explanation from Official Google’s Blog:
This morning, there was a routine maintenance event in one of our European data centers. […]
Unexpected side effects of some new code that tries to keep data geographically close to its owner caused another data center in Europe to become overloaded, and that caused cascading problems from one data center to another. […]
The bugs have been found and fixed, and we’re in the process of pushing out changes.
Definitely .. IT IS rocket science 🙂