Harbaugh needed to tell the quarterback who led his team to a Super Bowl just six years ago that he wasn't the best option to win now.
"I don't know if it was the hardest conversation, because in both of our minds we probably knew that the talk was coming at some point," Flacco said.
If it wasn't the hardest conversation, it was certainly the hardest decision of Harbaugh's 11-year run as Ravens head coach.
Harbaugh and Flacco have formed one of the most successful coach-quarterback tandems in NFL history. In 11 seasons together, they've won a Super Bowl, advanced to three AFC Championship Games and produced one losing season.
Their 106 victories (including playoffs) rank fourth among coach-QB combinations since 2008. The legacies of Harbaugh and Flacco have been intertwined like Belichick and Brady, Tomlin and Roethlisberger, and McCarthy and Rodgers.
Harbaugh's announcement wasn't simply about sticking with Lamar Jackson as the starter for Sunday or the rest of the season. This benching essentially signaled the end in Baltimore for Flacco, who has been by Harbaugh's side for every accomplishment he's had with the Ravens.
"We don’t make it about anything other than football," Harbaugh said this week when asked if his close relationship makes the decision tougher. "We keep it simple. It’s about football -- that’s what we’re here for."
The right business decision was for Harbaugh to keep starting Jackson. He's 3-1 as a starter and is one 48-yard, fourth-down heave by Patrick Mahomes away from being undefeated.
Jackson has brought an energy that helped end a three-game losing streak and propel Baltimore back into the playoff hunt. He's brought a much-needed identity to the offense, and he's the key figure in a winning formula of a strong running game paired with a dominant defense.
With Jackson, the Ravens have scored 27 points per game (eighth in the NFL) and rushed for a league-high 228.5 yards. Jackson's 336 rushing are the most by a quarterback in his first four starts in the Super Bowl era.
Harbaugh could have gone back to Flacco, insisting his former Super Bowl MVP gives the Ravens the better chance to push the ball downfield and provides more big-game experience. It would have been difficult for Harbaugh to stand in front of the players and say they're going back to Flacco (who won four of nine games) instead of Jackson.
A few weeks ago, Harbaugh indicated the two biggest factors with the quarterback decision were timing and circumstance. And by the time Flacco fully recovered from his hip injury, the Ravens were in the midst of playing their best football collectively as a team.
No one in the Ravens' locker room appeared surprised by Harbaugh's decision. The impression was that this was a mere formality.
"[Flacco] understands injuries are part of the game, and the timing is unfortunate," left tackle Ronnie Stanley said. "He understands Lamar has done a great job."
The Ravens know what they have in Flacco. Since winning the Super Bowl, he's 43-42 as a starter with an 82.7 passer rating (which ranks 37th out of 42 qualifying quarterbacks). That's the definition of mediocrity.
With Jackson, there is more of an unknown. He can break 20-yard runs. He can break away from a defender in the pocket and extend plays. There are growing pains, and the hope is he'll cut down on his turnovers and slide more often to avoid injury.
In the end, Jackson won the job more than Flacco lost it. The positives and the wins delivered by Jackson outweigh going back to the most successful quarterback in team history.
"I think it’s the best thing," Harbaugh said of his decision. "My gut ... I always hate to say ‘gut.’ If you’re thinking with your gut, really, is that really wise? So, how about my brain and my heart says, and my experience, that this is the way to go."