Quick answer
Getting what you wanted is sweet. The second line explains why fools will not turn, and the two halves are more connected than they look.
Read both lines
The first line repeats verse 12's observation about a longing satisfied, this time calling it sweet to the nephesh, the appetite and self. The second line then applies that fact to the fool's situation, and the logic is uncomfortable: turning from evil means giving up a desire, and giving up a desire is the one thing this verse has just said is hard. The fool is not depicted as stupid here but as unwilling to lose something sweet. That is a more honest account of why people do not change than calling them ignorant.
Related: Proverbs 13:12 · Proverbs 2:14 · Proverbs 26:11
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.