How to Drive Girls Crazy

Why does there always seem to be an inverse proportion between a man's creative genius and his ability to maintain a sane family life?

Exhibit #421453, from an otherwise charming little letter sent by F. Scott Fitzgerald to his daughter while she was away at camp:
I think of you, and always pleasantly; but if you call me "Pappy" again I am going to take the White Cat out and beat his bottom hard, six times for every time you are impertinent. Do you react to that?
Then, later:
P.S. My come-back to your calling me Pappy is christening you by the word Egg, which implies that you belong to a very rudimentary state of life and that I could break you up and crack you open at my will and I think it would be a word that would hang on if I ever told it to your contemporaries. "Egg Fitzgerald." How would you like that to go through life with — "Eggie Fitzgerald" or "Bad Egg Fitzgerald" or any form that might occur to fertile minds? Try it once more and I swear to God I will hang it on you and it will be up to you to shake it off. Why borrow trouble?
Or was he just being playful?