Quick answer
The difference starts before anyone speaks. What each person is turning over privately is already going in a different direction.
Read both lines
Both halves are about the interior, which is unusual for a pair of lines that could easily have contrasted actions. "Thoughts" and "counsels" are both planning words, so the verse is comparing two people at the same stage, before anything has been done, and finding them already separated. The second line's word for deceit is the same one used of dishonest scales at 11:1, which quietly connects a man's private reasoning to a merchant's rigged bag. What happens later in public was settled earlier in private.
Related: Proverbs 11:1 · Proverbs 12:20 · Proverbs 4:23
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.