Quick answer
Knowing more produces fewer words, not more. The verse pairs restraint in speech with a settled temperament.
Read both lines
The first line inverts what most people assume, that expertise should be audible. Sparing your words is a form of economy, and it implies a person who has decided what is worth saying. The second line adds temperature: a calm spirit, which the book has been recommending since it described the man slow to wrath as having great understanding at 14:29. Put together, the verse sketches someone who is neither loud nor quick, and it treats that combination as the visible form of knowing something.
Related: Proverbs 14:29 · Proverbs 10:19 · Proverbs 15:28
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.