In your opinion, what is the most dangerous* myth, story, tale, folklore, ect. for us (or maybe you) humans, and why do you say that?

* for those of you who are more focused and engaged than the statistical norm suggests, the similarity of this post to another I just made may seem jarring; however, if you have made it this far, you are also probably also aware that it ain't all the holy schnitz out there, there's piles of dirt surrounding every gold nugget, so you might as well flash the downs while you expose the ups.