Idiom for the need to expose oneself to something they don't believe in, to broaden the mind

As an example consider the following:

Atheists must read some religious literature now and then to make sure they are not trapped in their own filter bubble of thinking.

I remember hearing an idiom to capture this. Kinda like the idiom - "You must know your friends well, but your enemies even better."

Solution 1:

Before judging someone, walk a mile in their shoes

To spend time trying to consider or understand another person's perspectives, experiences, or motivations before making a judgment about them.

TFD

(As the jokes goes: because then you will be a mile away and they will have no shoes.)

Solution 2:

An informal phrase is

don't knock it until you've tried it - idiom

Definition of don't knock it until you've tried it —used to tell a person that he or she should try something before criticizing it https://www.merriam-webster.com/dictionary/don't%20knock%20it%20until%20you've%20tried%20it

You may be thinking of

The phrase "know thy enemy" comes from the ancient Chinese general Sun Tzu.

The full quote is:

"Know thy enemy and know yourself; in a hundred battles, you will never be defeated. When you are ignorant of the enemy but know yourself, your chances of winning or losing are equal. If ignorant both of your enemy and of yourself, you are sure to be defeated in every battle." https://answers.yahoo.com/question/index?qid=20090111114125AARe9kS