The entire operation hinges on the fact that the Lamanites had good intelligence about the size of Helaman’s army, and that when they were counted they were all found to be in the field. The secret deployment of the two units was unnoticed, and the Lamanites operated on their best intelligence. With the entire Nephite army in front of them, there was little need to defend Manti, as the battle would be final, and all Nephite opposition in this area should have been eliminated.