I don’t think LW claims that’s the only place irrationality comes from. There’s the various biases, an inability to update, akrasia, and so on...
Analogously,
Happy families are all alike; every unhappy family is unhappy in its own way.
Leo Tolstoy, Anna Karenina, Chapter 1, first line
Analogously,
Leo Tolstoy, Anna Karenina, Chapter 1, first line