A man that has lost a friend and patron may flatter himself that all his grief arises from generous sentiments, without any mixture of narrow or interested considerations: but a man that grieves for a valuable friend, who needed his patronage and protection
 David Hume, An Enquiry Concerning the Principles of Morals (1751). copy citation

Context

“Our predominant motive or intention is, indeed, frequently concealed from ourselves when it is mingled and confounded with other motives which the mind, from vanity or self-conceit, is desirous of supposing more prevalent: but there is no instance that a concealment of this nature has ever arisen from the abstruseness and intricacy of the motive. A man that has lost a friend and patron may flatter himself that all his grief arises from generous sentiments, without any mixture of narrow or interested considerations: but a man that grieves for a valuable friend, who needed his patronage and protection; how can we suppose, that his passionate tenderness arises from some metaphysical regards to a self-interest, which has no foundation or reality? We may as well imagine that minute wheels and springs, like those of a watch, give motion to a loaded waggon, as account for the origin of passion from such abstruse reflections.” source