The NASB throws in an editorial “should” in the second part of this verse. It doesn’t have a number to show the Hebrew word so I have to assume it is an interpretation.
(Proverbs 16:10 NAS77) A divine decision is in the lips of the king; His mouth should not err in judgment.I like it because it makes this verse have some logical sense. It seems odd to say that the king is always right. This would be a proof text for the Divine Right of Kings people.
I find it easier to understand with the “should” in there. I can find rationale for the word because of other verses that talk about how a king should rule in wisdom and wisdom starts with a fear of the Lord. We also need to allow for the possibility that God is working something out that we don’t see and would not understand if we did see.
So? Be careful before you criticize leaders. Just because you don’t agree with them doesn’t mean that they are not God’s agents. That hurts to say in today’s political climate but is still true.