A deliberate deception (misleading one’s colleagues, or a patient, or a boss) has at least one clear benefit. The person doing the deceiving will, by definition, recognize the deceit and will inwardly acknowledge the failure. Perhaps he will amend the way he does his job to avoid such a failure in the future. Self-justification is more insidious. Lying to oneself destroys the very possibility of learning. How can one learn from failure if one has convinced oneself —through endlessly subtle means of self-justification, narrative manipulation, and the wider psychological arsenal of dissonance-reduction — that a failure didn’t actually occur?
Syed, Matthew. Black Box Thinking: Why Most People Never Learn from Their Mistakes—But Some Do. Portfolio, 2015.
Putin’s unwavering belief that Ukraine would swiftly capitulate represents the greatest intelligence failure of his quarter-century tenure in power. He was furious when his invasion did not unfold as he envisioned, casting blame on and even arresting some senior security officials. But Putin had laid his own trap. Like many authoritarians, he had fostered conditions in which subordinates told him only what he wanted to hear. Intelligence, in its best form, encourages political leaders to ask the right questions, challenge their assumptions, and consider what might go wrong. Although intelligence officers have a professional responsibility to adapt to the interests, foreign policy priorities, and preferred briefing style of the leaders they serve, sometimes the highest form of service an intelligence agency can provide is to disabuse its political masters of a strongly held but false idea.
https://www.foreignaffairs.com/united-states/trump-breaking-american-intelligence
Over time, it becomes difficult to tell where self-delusion ends and dissembling begins. Eventually, after the words are repeated often enough, the distinction blurs and matters less, if at all. The two merge. An illusion endlessly repeated despite its demonstrable untruth ceases to be an illusion and becomes a lie; a lie endlessly retold can become second nature, so ingrained and instinctive as to detach from its origins and morph into self-delusion. American officials’ recurrent claims, over many decades, that they are committed to a two-state solution and that another round of U.S.-mediated talks could bring it about were no doubt born of genuine conviction. When, failure after failure, they continue to echo the mantra, it is no longer an illusion and turns into deceit. It is another of those phenomena one needs to experience to appreciate. American officials had faith when they went to Geneva and Camp David and also knew both would be a bust; believed in Kerry’s initiative and knew it was quixotic; trusted that Saudi-Israeli normalization was achievable and were resigned to the fact that, for the time being, it was a pipe dream. They both knew and did not know and were not sure which was which. “The past was erased, the erasure was forgotten, the lie became truth,” George Orwell wrote in his dystopian novel, 1984. Proof disproves belief, and still the faith endures.
https://www.foreignaffairs.com/united-states/lies-america-tells-itself-about-middle-east