Introduction to Cautionary Tales for Children

And is it True? It is not True.
And if it were it wouldn't do,
For people such as me and you
Who pretty nearly all day long
Are doing something rather wrong.
Because if things were really so,
You would have perished long ago,
And I would not have lived to write
The noble lines that meet your sight,
Nor B. T. B. survived to draw
The nicest things you ever saw.