Full Idea
What theory of morals can ever serve any useful purpose, unless it can show, by a particular detail, that all the duties which it recommends, are also the true interest of each individual?
Gist of Idea
No moral theory is of any use if it doesn't serve the interests of the individual concerned
Source
David Hume (Enquiry concerning Principles of Morals [1751], IX.II.228)
Book Reference
Hume,David: 'Enquiries Conc. Human Understanding, Morals', ed/tr. Selby-Bigge/Nidditch [OUP 1975], p.280
A Reaction
It is hard to disagree, even if occasional cases of extreme altruism can occur.