Psychology
You figure out how you feel by watching what you do
Daryl Bem argued that people often don't have direct access to their own attitudes, so they infer them the same way an outside observer would: by watching their own behavior. Smile because you're told to, and you'll actually feel a bit happier; volunteer once, and you'll start seeing yourself as a generous person. Bem proposed it as a simpler alternative to cognitive dissonance for many everyday attitude shifts.