For a team who looked remarkably fit all year, Donegal's fading efforts against Galway were difficult to understand.
For McGuinness, though, there was a sense of clarity. To get back to an All-Ireland final, Donegal required added firepower.
Against Galway, Donegal's six starting forwards scored just eight points between them. For McGuinness, there was a missing piece.
Enter Michael Murphy.
The All-Ireland winning captain under McGuinness in 2012, Murphy retired from inter-county football after the 2022 season and had been working as a BBC pundit before McGuinness called.
Like with McGuinness' return, Murphy's second coming did not guarantee success, but the 35-year-old worked hard to whip himself into shape and has flourished under the new rules.
Used intelligently by McGuinness - taken off early in wins over Down, Louth and Meath - Murphy has scored 0-44 in 10 championship appearances this season, significantly easing the burden on 2024 top scorer Oisin Gallen and allowing the management team to use McBrearty as an impact player in recent weeks.
Behind Murphy, the Donegal machine has operated beautifully. At the opposite end of the field, Shaun Patton has been brilliant in goal and Finnbarr Roarty has excelled at corner-back. Ryan McHugh has run himself into the ground from wing-back while Michael Langan has been a metronomic presence in midfield.