It's in the bylaws of the corporation typically. Feduce duty lawsuits are very common and it certainly isn't a "myth".
This is a special case where saying “business judgement rule” might not be enough to get Facebook out of trouble, though I’m sure Facebook’s lawyers will dispute that.
https://s21.q4cdn.com/399680738/files/doc_downloads/governan...
The lawsuits may happen, however they also almost never win.
https://corpgov.law.harvard.edu/2020/03/10/directors-fiducia...