The workers sang it as a dirge as they worked. Wall workers living outside the city spread the fear. Ridicule, scorn, open threat, disruption, confusion. They had become discouraged, and assumed a defeatist attitude because there was still so much work to be done. Discouragement is a part of the enemy's strategy to defeat work that honors the Lord.
Discouragement is accompanied by fear and doubt.
The will to continue the job fails because of emotional exhaustion and physical fatigue. The closer we live to the enemy camp, the harder it is to live by faith. It causes believers to doubt both themselves and God's power. From Numbers 13.33, when twelve men were sent by Moses to spy out the strength of the people in the Promised Land. Ten reported that the people of the land were giants, and in comparison the Israelites were like grasshoppers.