Quick answer
The first story always sounds true: whoever speaks first frames the facts. The proverb installs a waiting period between hearing one side and believing it.
Read both lines
First stories are not usually lies; they are curated, facts arranged by an interested party, gaps invisible even to the teller. Then the neighbor comes and examines him, and under questioning the seamless account develops seams. The verse is a one-sentence education in epistemic patience: the friend's account of the quarrel, the glowing reference, the outrage that arrives before the context. Belief is what you owe the evidence, and the evidence is not all in until the other side has talked. Its cousin is two doors up at 18:13; both protect the same treasure, a judgment worth trusting.
Related: Proverbs 18:13 · Deuteronomy 19:15–18 · John 7:51
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.