"In truth, O judges, while I wish to be adorned with every virtue, yet there is nothing which I can esteem more highly than the being and appearing grateful. For this one virtue is not only the greatest, but is also the parent of all the other virtues."
What does Cicero mean here when he says that gratitude is the parent of all other virtues? In the past, I have written about how having a grateful attitude can make you happier. Gratitude most certainly is a feeling of happiness or appreciation about benefits which you enjoy. But I doubt that Cicero saw gratitude as "only a stepping stone to personal happiness," to quote psychologist Robert Emmons.
In Pro Planico, Cicero sites the specific virtues arising from the positive feeling of gratitude, such as showing affection for one's parents, reverence, appreciation of friends, acts of kindness, and so forth. Gratitude often inspires us to do good things; this likely is what Cicero meant when he said that gratitude is the parent of all other virtues. Really it is fair to say that gratitude is both a happy feeling, and a behavior common to those of high moral standards. On the other hand, you are probably ungrateful if you do these 5 things: