Quick answer
The face reports on the heart. Gladness inside shows up outside, and sustained inner sorrow eventually breaks something structural.
Read both lines
The first line traces an ordinary and cheerful mechanism: what is happening at the center works its way to the surface, and the NKJV footnotes "countenance" as simply face. The second line is where the verse turns serious. The movement is the same, from heart outward, but the freight is grief, and the result is not a sad expression but a broken spirit, the same fracture 15:4 attributed to cruel words.
Read this as observation, never as instruction. The verse is not telling a grieving person to cheer up, and it does not suggest that a broken spirit is a failure of faith or effort. It reports what sustained sorrow does to a human being, which is exactly the kind of honesty that lets a suffering person feel understood rather than diagnosed. The wise response to someone whose face has gone quiet is attention, not a correction to their expression.
Related: Proverbs 15:15 · Proverbs 15:30 · Proverbs 17:22 · Psalm 34:18
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.