Smiles are probably the most underrated facial expressions, much more complicated than most people realize. There are dozens of smiles, each differing in appearance and in the message expressed.
Paul EkmanIn some instances, you may care so much about the person who has hurt you, or be so unable to be angry with him (or with anyone), that you rationalize his hurtful acts by finding some basis in your own actions for his hurtful behavior; you then feel guilty rather than angry. Put in other terms, you become angry with yourself rather than with the one who hurt you.
Paul EkmanIf a person feels terrible, it usually should not be shown or acknowledged during a greeting exchange. Instead, the unhappy person is expected to conceal negative feelings, putting on a polite smile to accompany the “Just fine, thank you, and how are you?” reply to the “How are you today?” The true feelings will probably go undetected, not because the smile is such a good mask but because in polite exchanges people rarely care how the other person actually feels.
Paul Ekman