P42: He who has benefited someone—whether moved to do so by Love or by the hope of Esteem—will be saddened if he sees his benefit accepted in an ungrateful spirit.

Dem.: He who loves a thing like himself strives, as far as he can, to be loved by it in return (by P33). So he who has benefited someone from love does this from a longing by which he is bound that he may be loved in return—i.e. (by P34), from the hope of Esteem or (by P30 S) Joy; so (by P12) he will strive, as far as he can, to imagine this cause of Esteem, or to regard it as actually existing. But (by hypothesis) he imagines something else that excludes the existence of this cause. So (by P19) he will be saddened by this.