Mill argues that people should act the way it brings them as much happiness as possible, and the only way they should sacrifice their own interests if their decision will bring more valuable common good than the personal one (Brink 2008).
In the situation when someone finds a wallet containing $300 Utilitarian ethics has a certain way of solving such a moral dilemma. As far as human should act the way it will bring him more happiness, but acting morally, if you know whose wallet it is than you have to act according to the principle: do as you would be done by. The explanation is very simple: if the moral principle’s purpose is to build good and virtuous society, than everyone would be happy and grateful to receive his lost wallet. But if you don’t know whose wallet it is than you can keep it, because the money you found will make you happy.
Brink, David. (2008). Mills Moral and Political Philosophy. The Stanford Encyclopedia of Philosophy (Fall Edition), Edward N. Zalta (ed.). Retrieved from: