What do I know about Distributed systems?

A distributed system is where components located on a network communicste by passing messages passing messages. The components interact with each other in order to achieve a common goal.

while some answer is fine, this is just an opener to a wider question the interviewer is trying to drive at. A good answer would briefly describe some theory of distributed systems and better bring out some experiences of building a distributed system. Preferably from personal experience OR definitely from something you have studied deeply.