What are John's reasons for not wanting to re-paper the room?

John believed that to give in and change the wallpaper would be giving into his wife's nervous tendencies. Once he changed the paper..... she'd find something wrong with something else.

At first he meant to repaper the room, but afterwards he said that I was letting it get the better of me, and that nothing was worse for a nervous patient than to give way to such fancies. He said that after the wall-paper was changed it would be the heavy bedstead, and then the barred windows, and then that gate at the head of the stairs, and so on.