Contradiction with Ecclesiastes 8:14
This verse notes the occurrence of righteousness being rewarded with what the wicked deserve, and wickedness being rewarded with what the righteous deserve, suggesting a contradiction to the notion that righteousness consistently leads to a sure reward.
Ecclesiastes 8:14: There is a vanity which is done upon the earth; that there be just [men], unto whom it happeneth according to the work of the wicked; again, there be wicked [men], to whom it happeneth according to the work of the righteous: I said that this also [is] vanity.
Contradiction with Job 21:7
This verse questions why the wicked often live and prosper, implying a contradiction with the idea that the fruit of righteousness is always a certain reward.
Job 21:7: Wherefore do the wicked live, become old, yea, are mighty in power?
Contradiction with Psalm 73:3
This verse expresses envy at the prosperity of the wicked, which contradicts the assurance that righteousness leads to a certain reward.
Psalm 73:3: For I was envious at the foolish, [when] I saw the prosperity of the wicked.
Contradiction with Jeremiah 12:1
This verse raises the question of why the wicked prosper, contradicting the certainty of reward for righteousness suggested in Proverbs 11:18.
Jeremiah 12:1: Righteous [art] thou, O LORD, when I plead with thee: yet let me talk with thee of [thy] judgments: Wherefore doth the way of the wicked prosper? [wherefore] are all they happy that deal very treacherously? [talk...: or, reason the case with thee]
Paradox #1
Proverbs 11:18 talks about the contrast between earning rewards through righteousness versus deceit. A potential contradiction or conflict here could be that it assumes everyone will always be fairly rewarded for their honesty and good deeds in life. However, in reality, sometimes dishonest people succeed and good people suffer, which might seem unfair or inconsistent with the promise of righteous rewards.