Imagine you were sitting on your couch. Suddenly a thought pops into your mind: what if an intruder comes through the door? The idea of someone taking something precious from you makes you feel afraid, so you get up and go to lock your door.
But by the time you lock the door it’s too late. You already let the intruder in. The intruder was never a person, it was a thought. The precious thing that was taken from you was your state of peace.
You acted on a scary thought instead of laughing at it, and for that moment, you thought you could lose what could never be lost.