Japanese culture makes allowances the occasional white lie, or tsumi no nai uso 罪のない嘘. This should not be confused with a condoning of fraud or malicious duplicity. But there are times when complete, stark honesty serves no productive ends—or so goes the mindset behind the expression baka shōjiki.
Suppose that an egotistical corporate manager asks his subordinates for their opinions of his latest marketing plan for the company’s products. A completely honest person might tell the manager that he thinks the idea is doomed to failure. But this would be self-destructive, and a textbook example of baka-shōjiki. The shrewd employee would realize that the manager was fishing for compliments, not criticism, and would restrain his urge to critique the manager’s ideas.
The English language is full of sports metaphors. How many times have you heard a colleague talk about “hitting a home run” with a sales presentation or “striking out” when requesting a raise? Ban-kuruwase is a metaphor from the world of sumo, a sport with which all Japanese are at least somewhat familiar.
Before a sumo tournament, the tournament officials post the ban-zuke 番付, which is list of the participating wrestlers and their respective ranks. When a wrestler is beaten by a lower ranking, this is an upset of the rank, or a ban-kuruwase.
Metaphorically, a wide range of unexpected events might be called ban-kuruwase: the unexpected promotion of a colleague at work, a flat tire on the way to an appointment, or even an unanticipated marriage proposal.