1. Letting Jose Mourinho Go
Of all the mistakes Roman Abramovich has made since his ownership began in 2003, letting Jose Mourinho go has to be chief among them. Chelsea fans will tell you that one of the darkest days in the Abramovich era was the day it was revealed "The Special One" would be leaving the club. The current Real Madrid coach remains the most successful Blues manager in history - he won back to back league titles, as well as the FA Cup and two League Cups, and the club have failed to find a manager who has made a similar impact since. Disagreements with Abramovich
reportedly left Mourinho on the brink as Chelsea manager, and his decision to drop Shevchenko for a number of high profile games supposedly angered the owner, who is a close personal friend of the player. Abramovich in the end let personal bias get in the way of business and the club lost one of their greatest ever managers as a result.
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