The fact is, when a human thinks of a password to use for themselves, this is a fundamentally insecure process. We have no cryptographic guarantees about the human brain like we do about a carefully-designed computer algorithm, and mounting evidence shows that humans are in fact quite predictable. One 2019 study found that by using a neural network, they were able to guess almost half of everyone's passwords in under 1000 attempts just by knowing a single one of that person's other passwords. It's only going to get worse from here.