https://en.m.wikipedia.org/wiki/Self-criticism_(Marxism%E2%80%93Leninism)
From the wiki:
"The Marxist concept of self-criticism is also present in the works of Mao Zedong, who was heavily influenced by Stalin, dedicating an entire chapter of The Little Red Book to the issue.
In some communist states, party members who had fallen out of favor with the nomenklatura were sometimes forced to undergo self-criticism sessions, producing either written or verbal statements detailing their ideological errors and affirming their renewed belief in the party line."
Quote from Stalin:
"I think, comrades, that self-criticism is as necessary to us as air or water. I think that without it, without self-criticism, our Party could not make any headway, could not disclose our ulcers, could not eliminate our shortcomings. And shortcomings we have in plenty. That must be admitted frankly and honestly."
Note: eliminate our short comings means murdering millions of people.