APAD: Every barber knows that.

Every barber knows that. 
"Every barber knows that" is a Russian proverb that means that something is very obvious or well-known. Barbers were traditionally seen as gossipers who knew everything that was happening in their communities. Barbers often hear a lot of personal information because of the intimate and trust-based nature of the client-barber relationship. The proverb refers to the idea that a person may think they are confiding something in someone, like their barber, but it is not a secret at all.

 The phrase highlights how a perceived secret is actually common knowledge, often because of the unique role barbers play in their communities.  It is used to point out the futility of trying to keep something quiet when it has likely been heard by many others.