Some excellent thoughts on Proverbs 26:9 (“Like a thorn which falls into the hand of a drunkard, so is a proverb in the mouth of fools“) by Pastor Jack  Hilton–

The effects of alcohol upon the physical body is the reducing and loss of sensitivity. The motor skills are dulled and the mental processes are slowed. The drunk does not sense pain as the sober person. If the drunk falls into the thorn bush and imbeds a thorn in his hand, he does not feel the pain and will not seek to remove the thorn. In like fashion the drunk can inflict great harm to the body that can lead to eventual death without sensing any great pain or danger of loos of life.

The fool because of the lack of wisdom and knowledge cannot know the value of a parable or piece of information regardless its true worth. The fool may scoff or scorn the information or simply ignore it altogether. His lack of mental sensibility greatly hinders or completely stops the understanding of the deeper knowledge keeping him from understanding the value or caring to seek the meaning of the parable. Since he senses no true value, he will forget the parable or corrupt its true meaning with his own opinion.

May God protect us from our own foolishness and ignorance and stir our hearts to seek after wisdom and knowledge that we may find the truth in all things.