To understand Aflac (NYSE: AFL), the first thing you have to realize is that the company does much more than just offer supplemental insurance in the U.S. market. Aflac’s primary business is in Japan, where it serves a larger market and produces more of its revenue and profit than its domestic operations do. Coming into Tuesday’s fourth-quarter financial report, Aflac investors wanted to see continuing signs of solid growth in revenue and earnings, but the insurer didn’t produce the growth in operating earnings that it had hoped to achieve.