Hmm... I am thinking of the conversation between the Little Prince and the Fox, where the Fox says that one must take responsibility for what one tames.

I think it has been so long since I read any of St Exupery's work to really recall what the admonition was. It was 30 years ago, I believe. I also recall in Night Flight that one of the Characters was admonished for the death of a pilot, and although the person had little to do with the death. The admonishing character later explains that what he did had little to do with right/wrong, but about making sure that pilots did not die.

Is that the admonishment to which you are referring?