The notion that working long hours and not taking holidays makes for a more productive workforce is, in my view, a managerial myth, with no foundation in organizational or psychological science.
That is why my wife and I decided to perpetuate the cultural myth of Santa Claus with our kids because their little hearts and minds seem to yearn for mystery and fantasy, and because we both seemed to gain more than we suffered from that well-meaning parental deception.
In my experience a great degree of tolerance is shown by Welsh speakers who, contrary to myth, will always speak English in the company of English monoglots however small a minority they may be within a group.
The final myth is the one that leads to the most pronounced false sense of security - that my make of computer or operating system is not vulnerable to security problems.