The narrator in "The Yellow Wallpaper" is the victim of a patriarchy, a male-dominated society. She is suffering from post-partum depression, but no one understands her emotional state or takes her complaints seriously, or at least not seriously enough.
The men in the work assume they know what's best for her. Her husband even forbids her from seeing her baby.
They do not understand that the narrator has a fertile and imaginative mind. By closing her away they are dooming her. When deprived of a legitimate outlet, her imaginative mind begins to see patterns in the wallpaper, and soon those patterns begin to reflect her own situation: that of a woman locked away, unable to free herself. And that is the picture and symbol of women in a patriarchal society.