IMO it's not Stava per se, it's the perhaps Inevitable point you reach when hammering yourself becomes not enjoyable.
Theres nothing wrong with hammering yourself, I used to do it, long rides, fast rides, push push push up hills, sweat like a pig...and I was grinning while I was doing it. Nothing wrong with that IF that's what you need or want.
But it wont always be what you need or want.
After an 82 mile ride one day, one I thoroughly enjoyed and probably averaged 16 mph, not bad if I say so myself....I suddenly lost the desire to put myself out there for hours on end...and that was it, I sat back, did 20 to 30 miles for the most part I stead of the standard 50 milers, knocked a mph off the average and all of a sudden refound the enjoyment.