It is just like English sayings and phrases, there are Japanese sayings and phrases as well. It is called [kotowaza ことわざ].

Today’s kotowaza

壁に耳あり商事に目あり。Walls have ears

KABE – WALL

SHOUJI – A PAPER SCREEN

障子・しょうじ・SHOJI

Original

There might be people who put their ears on walls to listen or make a hole on a paper screen to look.

Its meaning

When we talk about secret stuff we never know who is watching or listening so we should be careful.

An example

Ninki ga atte nakanaka te ni hairanai game o utteru mise wo mituketa. tomodachi ni kossori oshietanoni, gabe ni mimi ari, shoji ni me arida. itsuno manika mina ga shitteita.

I found a shop where we can buy a game which is really hard to get. I told my friend secretly but kabe ni mimi ari, shoji ni me ari. Before I knew it everyone knows about it.

arigato