The Home Forum essay on smiles, "Made in Japan," Sept. 4, is good for a tourist, but after living in Japan for 30 years and now teaching a college course on "Cultural Foundations of Japanese Business," I suggest a few deeper reasons behind them. Japan is a very homogeneous nation. It is not an immigrant country. Smiles come easier when it's all in the family, as it were.Japan is densely populated. Unless smiles greased the wheels of society, the friction would be unbearable. Smiles can cover embarrassment or, even worse, grief; Japanese do not wear their hearts on their sleeves. Smiles can be strategic: "When in doubt, smile." Walt Kelleher, New Orleans Letters are welcome. Only a selection can be published, subject to condensation, and none acknowledged. Please address them to "Readers Write," One Norway St., Boston, MA 02115.