Alex Ferguson's career as Manchester United manager mirrored Matt Busby's in so many ways but one thing he and the club will be determined to avoid is the decline the team suffered after Busby first retired in 1969.
United will strive to ensure that whoever follows Ferguson can keep the club at the peak of the English and European game so they do not suffer the decades of relative failure that followed the messy end of the Busby era 40 years ago.
Busby created the modern United out of the smouldering World War Two bomb wreckage that all but destroyed Old Trafford, then pulled himself and the club through the Munich air disaster that claimed the lives of so many of the Busby Babes in 1958 and eventually achieved glory by winning the European Cup in 1968.
But United rapidly declined after he retired in January 1969 to move upstairs as general manager and then as a director and in 1974 the unthinkable happened when they were relegated.
Six years after becoming champions of Europe, United suffered the humbling experience of playing the likes of Notts County, Oldham Athletic and York City in the second division.
The late George Best, who along with Bobby Charlton and Denis Law, inspired United to greatness in the 1960s, pinpointed the start of the decline as the night Busby achieved his lifelong ambition of winning the European Cup in May 1968.
"For Matt and Bobby Charlton, for Bill Foulkes, for Denis Law... they'd done it. And then they sat back, and you could almost hear the energy and ambition sighing out of the club. It was like being in at the winding up of a great company."
Busby announced his retirement on Jan. 14 1969 with United sixth from bottom of the old top flight first division.
With his 60th birthday on the horizon, Busby felt his life's work was done and United needed a younger man but there was no immediate successor to replace him.
Those who took on the challenge - Wilf McGuinness, Frank O'Farrell and later Tommy Docherty, Dave Sexton and Ron Atkinson - never came close to recapturing Busby's successes.