An idiom that means; those who control information have far more power than those with military force. It is actually a fallacy - Patton himself proved this. The idiom assumes the people are smart to begin with, an assumption that has been proven wrong countless times in history. And whoever said that has obviously never encountered automatic weapons anyway.
Somebody thinking he's smart: I control information! I control the people! The pen is mightier than the sword!
A realist: I control the weapons! Might makes right!