Quick answer
The crooked road is booby-trapped by its own nature. The person who guards his soul solves the problem by route selection: staying far from the road where the traps are laid.
Read both lines
The thorns and snares are not planted by an avenging hand; they are native to crooked ground. Deceit breeds entanglement, and the double life doubles its own tripwires. The second line's modesty is the wisdom: the one who guards his soul is not skilled at dodging thorns or brave among snares, he is far away, on another road entirely. This book keeps insisting that most moral victory is positional (4:14–15: do not even pass by the way of evil), and this verse explains why. Guarding your soul looks less like combat and more like navigation.
Related: Proverbs 4:14–15 · Proverbs 16:17 · 1 Timothy 6:9–11
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.