The culture of playing yourself down and praising others is considered to be modest and humble. Even I did not always appreciate this idea of Japanese virtue. I still sometimes take other Japanese literally, at face value, and make significant mistakes.
This concept of polite humility is at times inverted into a false polite complement to others. For instance, when a Japanese writes in an email, "It was a pleasure meeting you. Please give me a call." in Japanese, he may not really mean it. If you call him, you may get a cold reply.
Though I'm a Japanese, born and raised there, for some reason, my upbringing didn't encourage me to nurture modesty and humility. Frankly, I think I still haven't learned it. It still astonishes me, the extent to which this is ingrained. I was recently surprised by a young 9-year-old Japanese girl, who modestly announced "I am not smart." A masterful performance of humility; I knew she was an honors student.