EPISTLE LXXXI. On Benefits.
You complain that you have met with an ungrateful person. If this is your first experience of that sort, you should offer thanks to your good luck or your caution. In this case, however, caution can effect nothing but to make you ungenerous… It is better… to get no return than to confer no benefits. Even after a poor crop one should sow again… In order to discover one grateful person, it is worth while to make trial of many ungrateful ones.
Seneca Epistles 1-65, Translation by Richard Gummere. Loeb Classical Library.