John, the narrator's husband, is a product of his time; he has little understanding of his wife's mental state and how his actions are affecting it. At the end of the story, when she has essentially gone insane, he opens the door to her room and finds her "creeping" around the perimeter, where she has torn the yellow wallpaper away.
"For God's sake, what are you doing!"
I kept on creeping just the same, but I looked at him over my shoulder.
"I've got out at last," said I, "in spite of you and Jane. And I've pulled off most of the paper, so you can't put me back!"
Now why should that man have fainted? But he did, and right across my path by the wall, so that I had to creep over him every time!
(Gilman, "The Yellow Wallpaper," library.csi.cuny.edu)
Naturally, John has no idea that the narrator believes a woman to be trapped behind the designs of the wallpaper, or that she has now placed herself into that role. His complete failure to understand her feelings, coupled with what appears to be a complete mental breakdown on her part, is too much for him to handle, and he faints. In this way, he shows that he cannot understand her emotional state, and he becomes a physical obstacle for her to "creep" over instead of a mental or emotional obstacle.
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