"It's such-and-such a day because of this number and this number and it only happens once in a lifetime"
The most frustrating part about those posts is usually the entire analysis is correct, up until that last throwaway line "it will never happen again." Why do the authors feel the need to include it? In some cases the real answer is it won't occur for another thousand or ten thousand years, but that's not good enough? Of course some of the others (December has five Tuesdays this year) happen about half of all years and are complete junk articles, but I actually find the rarer ones kind of neat, with the exception of the completely erroneous disclaimer.