Every year before Sukkot I do a class with my juniors on happiness. We know that Sukkot is referred to as זמן שמחתנו (time of happiness), but what is happiness?
First I show them the following TED Talk by Daniel Gilbert:
Afterwards, I discuss with them Rav Hirsch’s comments on the words in the Torah “והיית אך שמח” regarding Sukkot. The basic idea of the TED Talk and Rav Hirsch’s comment is that happiness is a state of mind, rather than the result of (perceived) pleasurable activities. Here is the (very short) source sheet with Rav Hirsch and the משנה in Pirkei Avot: איזהו עשיר? השמח בחלקו.