Why did Lincoln agree to set aside the Anaconda Plan in favor of McClellan's strategy?

Initially, McClellan was trusted a military leader. He was able to successful train and equip the US military against the Confederacy. His planning proved to be detailed however, his perfectionist qualities made him slow to move and often without the aggression needed to fight the Confederacy. His plan was, theoretically, a good one in which troops would move east and come at Virginia from the water. This attack was aimed right at Richmond and if successful would have ended the war.