What is the proper way to foster generosity and gratitude?

I can see how generosity and gratitude are important as means to foster right resolve. But what if someone do good things sometimes due a sense of obligation, but also cause much harm to you? For example, this mother . Given that our resources and gains are limited, it is not much better to support the virtuous one rather than the unvirtuous? And in the case of supporting the unvirtuous and unwise, how this would not contradict others teachings like "do not associate with fools" and "give a gift in a proper time" ? (a unwise person would surely use a material gift unwisely causing harm for himself/herself and others).