belief

'Of course. Having allowed oneself to drift, unresisting, unpraying, accepting every half-conscious solicitation from our desires, we reached a point where we no longer believed the Faith. Just in the same way, a jealous man, drifting and unresisting, reaches a point at which he believes lies about his best friend: a drunkard reaches a point at which (for the moment) he actually believes that another glass will do him no harm. The beliefs are sincere in the sense that they do occur as psychological events in the man's mind. If that's what you mean by sincerity they are sincere, and so were ours. But errors which are sincere in that sense are not innocent.'

-CS Lewis, The Great Divorce, Page 38