(Basilisk Warning: may not be good information to read if you suffer depression or anxiety and do not want to separate beliefs from evidence.)
Having an internalized locus of control strongly correlates with a wide variety of psychological and physiological health benefits. There's some evidence that this link is causative for at least some characteristics. It's not a completely unblemished good characteristic -- it correlates with lower compliance with medical orders, and probably isn't good for some anxiety disorders in extreme cases -- but it seems more helpful than not.
It's also almost certainly a lie. Indeed, it's obvious that such a thing can't exist under any useful models of reality. There are mountains of evidence for either the nature or nurture side of the debate, to the point where we really hope that bad choices are caused by as external an event as possible because /that/, at least, we might be able fix.. At a more basic level, there's a whole lot of universe that isn't you than there is you to start with. On the upside, if your locus of control is external, at least it's not worth worrying about. You couldn't do much to change it, after all.
Psychology has a few other traits where this sort of thing pops up, most hilariously during placebo studies, though that's perhaps too easy an example. It's not the only one, though : useful lies are core to a lot of current solutions to social problems, all the way down to using normal decision theory to cooperate in an iterated prisoner's dilemma.
It's possible (even plausible) that this represents a valley of rationality -- like the earlier example of Pascal's Wagers that hold decent Utilitarian tradeoffs underneath -- but I'm not sure falsifiable, and it's certainly not obvious right now.
I second Evan that the warning was a good idea, but I do wonder whether it would be better to just say "content warning"; "Basilisk" sounds culty, might point confused people towards dangerous or distressing ideas, and is a word which we should probably be not using more than necessary around here for the simple PR reason of not looking like idiots.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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