What was I Scared of? by Dr. Seuss
The story concludes with the unnamed narrator realizing that the animated ambulatory night walking green pants are just as afraid of him as he is of them and the narrator and the pants become the best of friends.
I was not convinced by this conclusion when I was a child nor have I ever read this story to a child who agreed with the ending. Despite this, it is a great story and I am still surprised that the sentient pant genre never took off.