What does Proverbs 26:9 mean?

The book of Proverbs uses terms like "fool" and "foolishness" to mean those who reject godly wisdom, truth, and common sense (Proverbs 1:7; 3:5–8). When someone resists truth, they become numb to wisdom. Ideas that immediately catch a wise person's attention are missed entirely by the fool. This proverb illustrates this using the metaphor of someone so drunk they don't feel a thorn stabbing into their hand. The encounter makes no difference; it's as if it's never happened.

A secondary application may be related to an earlier proverb (Proverbs 26:7). A drunk person is clumsy; they won't be skilled at pulling slivers out of their hands. A person lacking wisdom might "have" a proverb—a general-case statement of wisdom—but they can't do anything with it. Merely memorizing words or repeating phrases doesn't make a person wise.

When the apostle Paul presented the gospel to Agrippa, Agrippa shrugged it off saying, "In a short time would you persuade me to be a Christian?" (Acts 26:28). Rather than being convinced, Agrippa was indifferent. Jude describes apostates as blaspheming "all that they do not understand" (Jude 1:10). They don't learn, they simply mock what they don't grasp. The apostle Peter writes about people who fail to accept the hard-to-understand things in Paul's letters. Peter writes that "the ignorant and unstable twist [those things] to their own destruction, as they do the other Scriptures" (2 Peter 3:16).