“ A man in a fit of anger, is actuated in a very different manner from one who only thinks of that emotion. ”
 David Hume, An Enquiry Concerning Human Understanding (1748). copy citation

Context

“All the colours of poetry, however splendid, can never paint natural objects in such a manner as to make the description be taken for a real landskip. The most lively thought is still inferior to the dullest sensation. We may observe a like distinction to run through all the other perceptions of the mind. A man in a fit of anger, is actuated in a very different manner from one who only thinks of that emotion. If you tell me, that any person is in love, I easily understand your meaning, and form a just conception of his situation; but never can mistake that conception for the real disorders and agitations of the passion.” source