Quick answer
Splitting the take costs more than it pays. The second line puts the accomplice in court, under oath, unable to speak.
Read both lines
Hates his own life is the book's idiom for self-destruction, and the first line does not say the partner is caught. It says the partnership is the injury.
The second line explains why, and it needs the legal background. The NKJV footnotes it as literally hears the adjuration, a public oath calling on anyone with knowledge to testify, with guilt attached to silence. Leviticus 5:1 spells that out: the witness who hears the utterance of the oath, knows the matter, and does not tell it bears the guilt himself. So the accomplice stands in the assembly, hears the oath pronounced, knows the answer, and says nothing. He is now trapped between perjury and betrayal, and either way he has spent something he cannot get back. The verse locates the damage in that moment rather than in the theft.
Related: Proverbs 1:10–19 · Proverbs 28:24 · Leviticus 5:1 · Proverbs 13:20
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.