The Lord commanded Israel to destroy all the peoples in the Land of Canaan, but on one occasion the Gibeonites approached Joshua and the leaders, persuading the Israelite leaders that the Gibeonites were not from Canaan. Joshua 9.14 says that the leaders of Israel did not ask counsel of the Lord. Later, Israel discovered the truth,

And it happened at the end of three days, after they had made a covenant with them, that they heard that they were their neighbors who dwelt near them…But the children of Israel did not attack them, because the rulers of the congregation had sworn to them by the Lord God of Israel. And all the congregation complained against the rulers… (Joshua 9.16–21).

Israel should have asked the Lord about the Gibeonites, and He would have told them the truth, but since they failed to consult Him, He let them suffer the consequences. They suffered in these ways:

They made a covenant with the Gibeonites, which if broken, as in the time of Saul, brought curses from God.
They were then obligated to protect the Gibeonites.
The congregation complained against the leaders.

The Lord knows everything. Therefore, let us pray to Him about everything, lest we suffer needlessly.