What drive threads, why do some go on and on, and others peter out quickly–

there are many factors at work, but what I have noticed is,
1) extended thread have topics that are broad– Streets ahead started broad, and then it became a cribbage thread. I have never played, don't have a clue about the game except it uses a cribbage board... So the thread be came less and less interesting...

2) some topics go off on tangents– and luck here, either the tangents are better than the original thread, or the thread soon breaks..
Fortnight comes to mind-- almost halted when tsuwm pointed out –Merkin– but went on to concepts about calendars– which make some sense– a word about an expression of time, goes off to discuss our concepts of time; when does a week start–, weekends, and then on to how the french express time and even to the french practice of policing concepts! (Isn't that what they are doing when they attempt to block words?)


my other obsession