"So the leaders partook of their provisions, and did not ask direction from the Lord. And Joshua made peace with them, guaranteeing their lives by a treaty; and the leaders of the congregation swore an oath to them." Joshua 9
Here we see Joshua sizing up a situation that seems so obvious and straightforward, that he doesn't think to seek God's will in it. However, the true story was entirely different than what Joshua perceived. This is a lesson to us that we cannot rely solely on our own senses and logic, but need to seek the Lord in all matters, even those that seem to be "no-brainers".