I assumed the "downhill" was all-inclusive; re his novels, he's never written one that IMneverHO caught "The Bitch" (as he has called a great novel), and I include NATD.
I'm sure he's been used as a dupe from time to time, and he's played the fool, intentionally and with relish (Advertisements for Myself, et al), and he's meddled with certain lives in such a way as to cause great unhappiness. All too true.
Art. Go figger.