You're facing down an evil beast, the terror of the seven seas, the last known living dragon, a man with the ability to freeze you into ice with his touch, or the smallest spider you've ever seen in your life that's minding its own business in the corner. Whatever the reason, you are terrified.
And your friend quickly assures you, "It's more scared of you than you are of it."
And in some cases, it's true, like the spider. You put it under a cup and take it outside and that's that. Of course, when you're saying it about the zombie demon, it might be more of a Blatant Lie
In the Merlin
episode Le Morte d'Arthur, Arthur assures a (nervous) Merlin that the best they are hunting is more frightened of them than they are of it. A giant, dragon-like beast then promptly attacks them.