Joshua was fooled into making a treaty with the Gibeonites because he did not consult God through the council already established in the Law, as outlined in Exodus 23:30-32. The Gibeonites disguised themselves and told a sob story instead of bringing the truth, similar to how false teachers will disguise themselves as good men and have only sob stories, not the truth, as referenced in various Bible verses. While Joshua was wise, his failure to consult God led to damage being done because he was not aware of the Gibeonites' true intentions, showing the importance of relying on God through established counsel.