If beliefs are swords, then Truth is an unbreakable sword. How to tell which swords are unbreakable, and which are just swords? We must repeatedly lay them down on the anvil and strike hard with any falsification that might break them.
The ones that shatter were not Truth; this is obvious enough. What some fail to see is the meaning of their own reluctance to put a cherished sword down on the anvil, and strike. That is not Truth, it just a belief you are not ready to let go of. To value Truth is to be prepared to acknowledge that you did not have it.