Query regarding a statement on information theory In the book "Information Theory, Coding and Cryptography" by R.Bose, it says that:

"Any information source produces an output that is random in nature. If the source output had no randomness, that is, the output were well known exactly, then there would be no need to transmit it."

I cannot grasp the meaning of this. What does it mean that an output is random? And why would there be no need to transmit the information if the output were known exactly?
Please help.
 A: If you could foretell the message perfectly, then no knowledge would need to be sent to you to reconstruct the message. For example, suppose the message were one period of a pseudo random sequence generated by a feedback shift register or something like a (very similar idea) Mersenne Twister and you knew the feedback links / recurrence relationship that would produce it. Then there would be no need to send the pseudorandom sequence to you - you could reconstruct it yourself.
Actually the quoted passage is giving you a definition of randomness and, in particular, of a random sequence, for the purposes of communication / information theory. Randomness is a property property that is relative to a certain observer / receiver / witness and it is the property of that observer's not being able to foretell a message that arises through that observer's ignorance. The information that needs to be sent to the observer is precisely the knowledge that that observer needs to reconstruct the message fully.
A: The point of the quote is that all the interesting data is random, that is to say, unpredictable. If there's anything predictable about the data, then the client can generate it without any interface to the real world. For example, there's be no point making a device that generates even numbers in ascending order because the computer can already do that without an interface to the real world.
