We play. The fun happens exactly when it intends to happen. Or what Gandalf said.Great sessions are great because they stand out from the rest; and they're also unpredictable in when and how they will occur. Much like a baseball game - when the first pitch is thrown there's no way of knowing whether it'll end up a 1-0 pitchers' duel or a 12-9 slugfest or a 10-0 blowout or a dull 3-2 game rife with fielding errors.
Some ball games end up great and memorable, others dull and boring, and the vast majority of them are in the middle somewhere. The same is true of D&D sessions.
Attempting to force any given session - never mind all of them - to be "great" is IMO a fool's errand.
I don’t think we have a fun throttle. Play is an organic thing for us. We play stuff happens. Dice are rolled. New situations emerge.
The whole of it is fun for me