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

鬼の目にも涙　Oni no me nimo naamida

Oni – a deman

Namida – tears

Even the hard-hearted can be moved to tears

Its origin

Even a cruel demon cries.

Its meaning

Even a person who is not caring usually, he/she sometimes becomes caring person.

An example

My teacher is well-known as a strict teacher at my school. But when my class won a choir competition he cried over the joy. Oni no me nimo namida da.

arigato