Hansei is an idea within the Japanese culture that is about acknowledging our mistakes and pledging improvement. In other words, our self-awareness is the first step for improvement.
In the hansei process, the emphasis is on what went wrong and on creating and developing corrective and preventive actions to assure that it does happen once again and has to be done constantly and consistently. In the Toyota Corporation if you succeed in a project, there is a meeting called hansei-kai that consist on reflect about what went wrong. If an involved employee claims that there were not problems with the project, they will be reminded that no problem is a problem. Thus, if you have not objectively evaluated the project to find opportunities for improvement, you will not be adapted to the hansei culture.
In Japanese companies it is a very common practice for a manager to expect hansei from his team in case of mistakes. The manager will assume the responsibility for the mistake and, meanwhile, his team will work on solving the problem.
Hansei also adds the concept of greeting success with humility. Stopping hansei, means stopping to learn. With the hansei culture everyone feels the need that there is always more room for improvement.