In the story The Yellow Wallpaper by Charlotte Perkins Gilman

Did you mean why the narrator was writing in secret?

John gives the narrator tonics and medicines to help with her recovery, but primarily directs her to stop writing. According to Weir Mitchell’s theory, any sort of creative activity will have a detrimental effect on the patient. The narrator does not agree with this part of her treatment and hates not being allowed to write while she rests; she suspects that work would actually speed her recovery. She has been writing occasionally in a small journal, but it is exhausting to do so in secret.