#4 His appointment of David Moyes
Very rarely do great men get to leave on their own terms (just ask Wenger) and even rarer do they get to pick their successor, but Sir Alex Ferguson was a lucky man in that he got to do both, winning the Premier League title in his last season, as well as appointing compatriot David Moyes to be his successor as 'The Chosen One'.
David Moyes had won steady acclaim for his 11 years work at Everton where he helped build the Merseyside outfit into a compact Premier League team, steady finishing as best of the rest without breaking the grip of the then hallowed 'big four'.
To state that David Moyes' reign as United boss was a disaster would be doing him favours, as under his watch, United went about breaking all manner of unwanted records, almost on a weekly basis, in a way not seen before (although they are on their way to those lows this season).
The club played dourly unattractive football (another similarity to the current bunch), and struggled woefully in the league, failing to make it to the top four for the first time in over 20 years at the end of the season.
In hindsight, Moyes' appointment was a disaster waiting to happen (one which still affects the club), as there is a distinct difference between managing an average side and one of the biggest clubs.
David Moyes' appointment set United back by years, as they fell further behind their rivals who had more sophisticated managers. Having solely taken the decision of hiring him, Ferguson deserves some of the blame for United's current struggles.