Self-criticism is the evaluation of past mistakes in order to learn from them. According to Lenin:
A political party’s attitude towards its own mistakes is one of the most important and surest ways of judging how earnest the party is and how it fulfils in practice its obligations towards its class and the working people. Frankly acknowledging a mistake, ascertaining the reasons for it, analyzing the conditions that have led up to it, and thrashing out the means of its rectification—that is the hallmark of a serious party; that is how it should perform its duties, and how it should educate and train its class, and then the masses.
— Vladimir Lenin, "Left-wing" Communism, an Infantile Disorder, 1920