"Even really at that point, that's just making the club," Mattingly said. "You can't really have a letdown at that point, and say, 'I made the club, life is good.' You have a couple of bad starts and somebody else is coming up. This is continual growth."
As the evaluation process continues, here's five players to watch over the final week.
OF Cole Gillespie: Out of options, the 31-year-old is competing for a backup outfield spot. Gillespie was solid as a reserve in 2015, batting .290 in 67 games. He's also enjoyed a strong Spring Training, entering Wednesday hitting .370.
The organization doesn't want to lose Gillespie, and is striving to find ways to keep him. He can play all three outfield spots and is also taking grounders at first base.
"It's tough that I can't really see what's happening in the future," Gillespie said. "I can't worry about that. All I can do basically is go out and play as hard as I can and help my team. I feel like whenever you do that, the rest will take care of itself."
INF/OF Derek Dietrich: Also out of options, Dietrich is a left-handed hitter with power. Since joining the organization in 2013, he has moved around from second base to third base to left field, and he's seeing time at first base. It will come down to if the Marlins feel he is the right bench fit with the potential to be an everyday player. Dietrich also could be a late spring trade piece.
RHP Edwin Jackson: If not in the rotation, which seems likely, Jackson's role could be either long relief or perhaps a setup role at some point. He adds value in several areas.
"He's messing around with a cutter now," Mattingly said. "It looks like it might be a good pitch for him."
LHP Brad Hand: Another player who is out of options, so he either makes the Opening Day roster or he may be designated for assignment or traded. Hand has bounced around as a starter and long reliever, but he may wind up as a situational lefty.
RHP Dustin McGowan: A 12-game winner as a starter with the Blue Jays in 2007, McGowan is a non-roster invitee who has impressed with a 95-plus mph fastball.
"All you can ask for is to pitch well, stay healthy, and if the opportunity arises here, great," McGowan said. "But you also are almost showcasing yourself for the other teams, too."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.