2 Kings 7

 "For the Lord had caused the army of the Syrians to hear the noise of chariots and the noise of horses—the noise of a great army; so they said to one another, “Look, the king of Israel has hired against us the kings of the Hittites and the kings of the Egyptians to attack us!” Therefore they arose and fled at twilight, and left the camp intact—their tents, their horses, and their donkeys—and they fled for their lives." vv.6-7 

Read chapter 7
At the same time as the four lepers rose at twilight to go to the Syrian camp is when the Syrians fled.  At the sound of a great army the whole army of the Syrians fled.  It so dumbfounded them that they didn't even take their horses that would have made their fleeing faster and surer.  They didn't even think to send some to seek out who the noise might be nor did they have the slightest bit of courage to face and defend themselves.  Yet all they conjured up in their minds was not real but a fear the Lord instilled in them just at a sound He made them to hear.  "God can, when he pleases, dispirit the boldest, and make the stoutest hearts to tremble. They that will not fear God, he can make them fear at the shaking of a leaf" (Benson Commentary).  How can illusion cause you to fear or lack trust in God?  How can you let God's truth discern from our own minds and what we hear or see?  Give a specific example.