Personal beliefs don’t have to reflect truths about reality – instead, they often reflect behavioural, societal or environmental demands.
For example: society tells you to judge a certain behaviour or desire. Because of this societal demand, you adopt a story or belief about why that behaviour is morally bad or to be misjudged. I think this is kinda similar to postdictions, so the cognitive mechanism that makes a person rationalize a given fact after it occurred.
And often we adopt beliefs because we believe they are beneficial for us, not because they are true. E.g., we think we shouldn’t grind and stop working, because we already did enough - but instead, we first wish to stop working and then rationalize this, to have a good reason to stop. On the other hand, we sometimes think that we are sabotaging ourselves and need to pull through to achieve great chiefs. In this case, holding contradictory beliefs can be useful.