It's clearly not true in all circumstances. You can bet that an airline pilot has a very clear idea of what they are doing, and so will your dentist. Closer to

It's clearly not true in all circumstances. You can bet that an airline pilot has a very clear idea of what they are doing, and so will your dentist. Closer to home there are plenty of sub-fields in software where I'd be completely lost but when (say) we have to add a new endpoint to the webservice I work with, I absolutely don't have to make it up as I go along. Your assessment of why people like to believe this seems spot on.