Well-run clubs never need to rebuild; they simply reload. It's an old maxim and it's generally true. If you're a dominant side, you maintain that dominance through continuous small changes rather than periodic blow-ups. Get the small changes right and you won't need to rebuild.
But for every rule, there's a counterargument: Juventus' run to the Champions League final, after they dispatched a young and vibrant Monaco side in the semifinals on Tuesday, is Exhibit A. When they take the pitch in Cardiff, assuming Sami Khedira recovers from injury, it could well be that Gianluigi Buffon and Leonardo Bonucci will be the only holdovers from the side that lost the Champions League final to Barcelona two years ago.
Sure, had Giorgio Chiellini not been injured for the 2015 final, it would be three out of 11, but it's still a pretty staggering turnaround in just two seasons. Indeed, 12 of the 18 in the matchday squad that day have now left the club.
Contrast this with their opponents that day, Barcelona, who have shed six. Or, for that matter, Real Madrid, who also lost six players (if you want to count Alvaro Morata, who left and came back, it's seven) from the side who won the trophy in 2014. You have to go all the way back to Chelsea in 2012, five years and five managers ago, to find a Champions League winner that has changed more than Juve have in the past two seasons.
You simply can't weather that much change unless you're a well-run club. And that goes beyond the manager, Massimiliano Allegri, right up to the higher reaches with sporting director Fabio Paratici and chief executive Beppe Marotta.
Not only have they rebuilt on the fly, they've done it twice in two seasons. In the summer of 2015, they lost Carlos Tevez, Andrea Pirlo and Arturo Vidal. Last summer, it was Paul Pogba and Morata.