Abstract: For a long time, "the leftist" mistakes we have committed took their epistemological root in the three over assessments: first, the over assessment of the social development phase in China|second, the over assessment of the development phase of human society|third, the over assessment of the goodness of human nature. The three misconceptions still exist in the inner mind of some people and have obstructed the sustained development of economy and society in our country. Therefore, it is essential for us to overcome these illusions in the spirit of proceeding from actual condition and seeking truth from reality.