How many managers have stayed at a top club for more than 15 years straight and cleaned up trophies left right and centre? Busby, Fergie and Shankly obviously. Wenger and Clough have the time span but lack a consistent trophy haul throughout their careers. There might be a select few in the other big leagues, but they are a ridiculously rare breed.
What are the odds that the first manager we bring in after losing the greatest ever turns out to be another 1000+ total games, tens of trophies, once-in a lifetime type manager? There's been a just handful of managers in the history of football who have done anything remotely close to what Sir Alex did here, and that's being generous to the other managers. Giving Moyes time and expecting him to eventually come good is like expecting to win the lottery twice in a row with the same numbers. It just doesn't happen, and thinking it does is overly romantic and naïve. Successful teams in today's football are the ones who continuously change managers and keep bringing in fresh ideas to build on the foundations at the club, like Mourinho has done at Chelsea and Pep has done at Barca and Bayern. Stability is overrated. There are more successful clubs out there who change managers every 2-5 years than there are successful clubs who stick to the same manager for 10+ years. Heck, the two most successful clubs in Europe at this very moment (Barca and Bayern) have had a combined total of 12 managers in the last decade.
"Stability = success" is not necessarily true. The right manager is what brings success, not the wrong manager for several years. We can remain successful even if we bring in new managers every now and then. If we keep giving the wrong guy more time than he deserves because of some old-fashioned idealism things will start going downhill really quickly, as we can see from our current season.
Call me a cynic, but if I knock my head against the wall and it hurts, I won't keep doing it to see if the pain eventually goes away. Plenty of clubs have sacked a manager who was wrong from the start and come out looking better because of it. I think that's becoming the case here too. The only question is whether it happens now or in May. The way this season is going, I can't see any sense in keeping him longer. We're in a downward spiral and need to abort. Moyes isn't doing anything on a fundamental footballing level to change our trajectory, and all money in the world won't change a thing until he realizes that the players aren't the problem.