So it was up to Mattingly to answer questions about what went wrong in this year's National League Division Series and how to fix it, after he and his coaching staff met with Colletti and his baseball-operations lieutenants to review the club.
Although Mattingly received a multiyear contract extension in January, one question he didn't answer conclusively was whether the club was bringing him back next year, although all indications are that it will.
"I'm assuming," he said. "Came to work, like every other day, nobody told me any different."
He said he "would be surprised" if there were a new general manager for him to work with.
"I came in today and it seemed like business as usual," he said.
Mattingly wouldn't give a definitive answer on whether his coaching staff would return, saying only he was "proud of everything we've done this year."
Mattingly did downplay disappointment over the way things ended in St. Louis this week, accentuating his belief that 2014 was another positive step in a multiyear process for rebuilding all phases of the organization.
"I don't feel like it's a bust," he said. "Win or bust is pretty tough. I don't mind that mentality, but you have to have reality, too.
"The playoffs were different this year. We didn't make an error. We had one baserunning mistake on a funky hop. They got the key hit, they made the key pitch and that's the difference in the series. We got beat, but we didn't beat ourselves. I can handle getting beat. I don't like losing. The things I always talk about, making the play, getting the hit, getting the out. They were able to do it. We weren't."
Mattingly said the one decision from the series with St. Louis he'd like to do over was bringing in lefty Scott Elbert to start the seventh inning of a tied Game 3 and face right-handed hitter Yadier Molina, with two left-handed hitters to follow. Elbert allowed a double to Molina, Jon Jay bunted him to second and Kolten Wong homered. Mattingly mentioned Brian Wilson as the likely right-hander for that situation. Wilson had warmed up before Elbert.
Mattingly conceded that managing the egos in this particular clubhouse "was trying a little bit ... a little challenging," mostly involving the crowded outfield.
"That was hard," he said. "I thought it would be easier. It wasn't. I had to make a decision. When they got banged up, it was easy. When everybody was healthy, I made the call. It wasn't four [Yasiel Puig, Matt Kemp, Andre Ethier and Carl Crawford]. It was five [with Scott Van Slyke]. And five turned into six with the kid [Joc Pederson]."
However, he disputed critics of the clubhouse chemistry.
"All year we battled that talk, but in September the team was ready to play," he said. "I don't worry about the chemistry. We went into the [Division] Series thinking we'd win, prepared to win. The guys were all-in, and got beat."
Though he wouldn't opine on Hanley Ramirez returning, Mattingly said it was his opinion that the shortstop was bothered by the uncertainty of looming free agency.
"It's almost impossible not to," Mattingly said. "It was the same to me last year [as a lame-duck manager]. It's just noise. You feel you're tough, but it's still there. It's there all year."
Mattingly said the baseball-ops department is concerned about the aging of the roster. Of the eight position starters, six are 30 or older.
"You see teams all the time, all of a sudden, they're old," he said. "At 32, 33 is old again, it always has been except for a 10- or 15-year period. It's something you should pay attention to. But it's what the owners have talked about, building the farm system so you don't have to do it with free agents."
He reeled off the names of the club's top prospects -- Pederson, Corey Seager, Julio Urias, Scott Schebler, plus rookie pitchers Pedro Baez and Carlos Frias.
"That's how to avoid that and what we're working toward. It's an invisible part because we don't get to see it."