Quick answer
Work the ground in front of you and you eat. Chase emptiness and you get a full measure of nothing.
Read both lines
The wordplay is the craft and English keeps some of it. Both halves use the same verb for being satisfied or having one's fill, so the man who tills is filled with bread and the man chasing vanities is filled with poverty. Everyone in the verse gets a full portion; the only question is of what.
The book said this at 12:11 with a different second line, where the man following frivolity is "devoid of understanding." This version drops the diagnosis and reports the result instead, which is bleaker and funnier. The exclamation point in the NKJV is doing honest work. Notice too what the first line asks for and does not ask for. It is his land, the ground already in front of him, and the verse says nothing about ambition, scale, or opportunity. The whole instruction is to work the thing you actually have.
Related: Proverbs 12:11 · Proverbs 28:22 · Proverbs 20:13 · Proverbs 24:30–34
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.