Quick answer
The fool's problem is not a weak mind but a misplaced delight: he does not enjoy understanding, he enjoys broadcasting.
Read both lines
The first line locates folly in the affections: the fool is not unable to learn but uninterested; comprehension bores him. The second line names what delights him instead: expressing his own heart, airing whatever is inside regardless of quality, transmission without intake. The verse stands next to 18:1 on purpose: the isolated man silences other voices by distance, the fool drowns them by volume, and both end in the same sealed room. Delight is the tell. What a person enjoys in conversation, hearing or being heard, is a fair map of which direction they are growing.
Related: Proverbs 12:23 · Proverbs 17:28 · James 1:19
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.