The same happens with people, when we give them an idea, a thought process, an alternative way to live a life, we might think they are dead in terms of reflecting back, but if we keep watering them with the right exposure of sun (which translates to beneficial, conceptual knowledge) along with constant duas then we never know that Allah, Who takes out living from the dead might turn them into plants bearing beautiful fruits.
The only thing, we as dawah carriers should do is sincere efforts, keeping in mind the result is in Allah’s hand alone, and not belittling anyone or any consistent effort.