The gatekeeper soldier senses someone's presence but dismisses it as "just my imagination," when it's actually not his imagination at all.

At night, a soldier named Shurath stands guard at the gate of a nobleman's mansion. He senses the presence of someone and raises his spear, but quickly thinks "It must have been my imagination..." and lowers his guard. However, it was actually not his imagination at all. Wake up, Shurath!