The Mesillas Yesharim in the seventh perek says:
The two reasons for acting cheerful despite how you really feel can be restated succinctly, albeit pedantically (1). Our affect (2) affects (3) the people around us, so affectation (4) might be a civic duty. Sometimes, affectation is the best way to effect (5) change in our own emotions.
1. Pedantically: Characterized by ostentatious display of formal scholarship.
2. Affect (Noun): the observable manifestation of feelings.
3. Affects (Transitive Verb): influences or causes change
4. Affectation (Noun): the display of feelings not genuinely felt
5. Effect (Transitive Verb): cause or bring about, especially used in overcoming resistance.
Rabbi Moshe Goldberger, of the Yeshiva of Staten Island, wrote the following:
I saw these ideas presented very well in a video by Dennis Prager, here. Just ignore the distracting graphics; they're for minds molded (tarti mashma) by the x-box and music videos. (Dennis Prager went to Yeshiva of Flatbush and RJJ, and his brother is Orthodox, but he is no longer observant. I assume he is aware of the two references above. Mr. Prager is not only fluent in Russian, but he can also read Hebrew backwards as well as he can forwards, a skill he developed while trying to kill time at RJJ.)