'Unable' in the Bible

When the king of Moab realized that the battle was going strongly against him, he took 700 expert swordsmen to attempt to break through to the king of Edom, but was unable to do so.

"Don't let Hezekiah deceive you, because he will prove to be unable to deliver you from my control. And don't let Hezekiah make you trust in the LORD by telling you, "The LORD will certainly deliver us and this city will not be handed over to the king of Assyria."