One of the defining features of the Japanese people is humility, known as kenson (ken-sohn). This manifests itself in interesting ways, most commonly in the form of Japanese people vehemently denying compliments paid to them about how good their language skills are, how attractive they look, and so on. It's a trait found in a lot of anime characters, like Madoka Kaname from the new (dark) magical girl series Madoka Magika, who in one scene describes herself as "thick-headed, lacking any positive character traits whatsoever." You might think of this as a cute caricature of actual Japanese personality types, but in my long years living in Japan and teaching ESL, I've encountered no small number of people like this, who felt it necessary to make it known how useless and/or baka (stupid) they were, for reasons that were difficult for me to understand. I've been told this kind of self-effacing personality is known as "the Dazai Spirit," after Japanese writer Osamu Dazai who penned such work as Ningen Shikkaku (No Longer Human) and Run, Melos! The concept can be encapsulated with by the ASCII [ Orz ] which represents a person kneeling low with humble apology, seen often on the Japanese interwebs.
A "low-to-the-ground" attitude of humility is especially important when interviewing for a job, something I've observed from both sides of the interviewing table during my time here. In a Japanese-style job interview you hand in a rirekisho, a standardized resume form which contains all important information about you, including school and work background, any certificates or qualifications you've obtained, plus your personal interests. During the interview, the job applicant essentially erases their personality entirely -- the Japanese word is jibun wo korosu, lit. to kill your 'self' -- presenting a calm, unemotional exterior while the interviewer asks questions. It's common for the interviewer to ask the applicant to list what they consider their personal strengths and weaknesses to be, and most Japanese will falter visibly when trying to come up with things they're especially good at. One thing I've noticed is that Japanese who have been overseas for a few years lose this natural humility. In the case of my wife, she attended a business school in California where they taught students to present their achievements in a proactive way to catch the eye of potential employers, but this approach was less than successful for her when she came back to Japan.
In Japan it's considered a good thing to be humble and self-effacing.