Ralph Kirkpatrick, Interpreting Bach's Well-Tempered Clavier: A Performer's Discourse of Method
(New Haven: Yale University Press, 1984), p. 125:
It is easy to mistake self-indulgence for inspiration. All religious disciplines know that it is sometimes exceedingly difficult to distinguish between the voice of God and the voice of the Devil. No matter how much we listen to our inner voices, we need to listen to other people's voices too in order to make sure that we have been genuinely inspired, not merely self-indulgent.