The same doubled construction 19:16 used: the guarding man is himself guarded, in the same verb.
Quick answer
Watch what you say and you will spare yourself a great deal. The verse repeats one verb on purpose.
Read both lines
The Hebrew uses shomer twice, once for what the man does to his mouth and once for what happens to his nephesh, his life. That is the same construction 19:16 built on, where keeping the commandment kept the man, and the repetition is the whole argument compressed into grammar: the guarding and the being guarded are one action. What the verse promises is modest and worth having. Not wisdom, not honor, just fewer troubles, and the plural suggests the ordinary accumulating kind rather than catastrophe. Most of what a mouth costs a person arrives in that form.
Related: Proverbs 19:16 · Proverbs 13:3 · Proverbs 12:10 · Proverbs 18:21
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.