Where is it written that lives should have a meaning?

Those words had an unpleasant effect on me. As if she were giving dispassionate advice, she was suggesting that I separate also from my third child. She seemed to be saying: Imma would be better off and so would you. I replied: If Imma leaves me, too, my life will no longer have meaning. But she smiled: Where is it written that lives should have a meaning? So she began to disparage all that struggle of mine to write. She said mockingly: Is the meaning that line of black markings that look like insect shit? She invited me to take a rest, she exclaimed: What need is there to work so hard. Enough.

—from The Story of the Lost Child, by Elena Ferrante.

Where is it written that lives should have a meaning?

Where?