No man is an island, and no Major League club has its fortunes dictated by the performance of a single man.
But one man can, nonetheless, still have significant sway.
With that in mind, we present five players who, after downturns on the field, need to get it together and perform at their peaks in order for their teams to realize their full potential in 2012:
Hanley Ramirez, Marlins The Marlins could have one of the more dynamic left sides of the infield in all of baseball, or they could have one of the more combustible left sides of the infield in all of baseball.
Ramirez is the X factor.
FIVE TO WATCH
MLB.com identifies and examines five players to watch in various categories this season:
Between 2006-10, Ramirez was simply one of the best players in the sport, batting .313 with a .906 OPS and averaging 25 homers, 40 doubles and 39 stolen bases in that span. His season in 2009, when he had a National League-leading .342 average with 24 homers and 106 RBIs, was MVP-worthy.
But in 2011, Ramirez appeared in just 92 games, batted .243 with a .379 slugging percentage -- the latter 151 points below what had been his career norm -- and underwent surgery on his left shoulder.
When the Marlins signed shortstop Jose Reyes, there was quite a bit of hand-wringing over how well Ramirez would handle the shift to third base, and that may well become an issue at some point. For now, Ramirez seems content with his role. That's huge for the Fish, because if Ramirez approaches his past numbers, he can make a dramatic impact on the NL East pennant race.
"He's healthy, that's the main thing," manager Ozzie Guillen said. "When Hanley is healthy, he can be one of the best hitters in the league. I think right now, he's having fun. ... Our goal is to keep him that way."
Carl Crawford, Red Sox The Red Sox didn't blow their Wild Card cushion last year because of a lack of offense, and Crawford's fall from grace didn't bring down an offense that led the Majors in runs scored.
But for Boston to reach its potential, Crawford has to reach his.
Crawford's Red Sox debut could not have gone much worse. Signed to a seven-year, $142 million contract, the expectations on him were high. When he struggled out of the gate and was moved down in the batting order, he placed even more pressure on himself to hit his way back to the upper third. None of it worked, and a nagging wrist injury that required offseason surgery sure didn't help.
The final tally? A .255 average, .289 on-base percentage, .405 slugging percentage and 18 steals. It was a far, far cry from Crawford's old, dynamic self.
Now that a setback in his recovery from the wrist surgery has affected his Spring Training schedule, leaving his Opening Day readiness in question, Crawford has another uphill battle ahead of him. He hopes -- and his team hopes -- that last year was an aberration in an otherwise stellar career, and that the internal and external pressures he faced -- and ultimately couldn't beat -- won't continue to drag him down.
"It's not even about showing people I can still play," Crawford said. "It's about proving to myself that I can still play. My goal is just to get back to being the person I was -- running again, going the other way, playing good defense."
Adam Dunn, White Sox You could make an argument -- a strong one -- that Dunn is coming off the worst year for an established star ... ever.
After a few years of settling into the big leagues, Dunn simply became one of the game's most bankable commodities from 2004-10. He was good for about 40 homers with more than 100 RBIs and 100 walks each and every year. Yes, he struck out a ton, and he certainly wasn't a defensive asset, but his power and his walks made him plenty valuable.
So the White Sox signed Dunn to a four-year, $56 million contract and put him in what seemed to be his most natural position -- designated hitter. But in 2011, he shockingly became a designated out.
Dunn hit .159 in 496 plate appearances. Had he reached 502 plate appearances, he would have qualified for the batting title, and his average would have been the worst ever for a qualifier in the modern era.
The White Sox have a younger roster this year, but Dunn -- and his unmovable contract -- remains. Few are counting the Sox as a legitimate contender this season, but given how much time and money they still have invested in Dunn, a return to his old self would surely be a positive development as they move forward. The good news is that he seemingly has nowhere to go but up.
"People will still talk about ," Dunn said, "but I want to give them a reason to talk about 2012."
B.J. Upton, Rays It's hard to believe that Upton -- the longest-tenured member of the Rays -- is only 27. But that's how it goes when you have your big, breakout season at 22 and then become a postseason star at 23.
The trouble for Upton is that repeating what he did in 2007 and '08 has been a bit of a struggle.
Not a monumental struggle, mind you. Frankly, if Upton repeats a 2011 season in which he hit 23 home runs, swiped 36 bags and drove in 81 runs, that's still a pretty darned good year.
But Upton is such a great athlete that it's impossible not to hope for truly elite output from him. If he can improve on a batting average that has hovered around .240 the past three years, all his other numbers will improve with it, and he might jump into that category.
And on a Rays team built around young starting pitching but in need of some offensive boost, Upton has the potential to lift his club to another level. Rays manager Joe Maddon, for one, believes Upton is arriving at the "sweet spot" of his career.
"When you have all those expectations attached to you as a young player, we have no idea what that looks like, what that means," Maddon said. "And he's had that and he's had to do a lot of his learning right here."
Jayson Werth, Nationals The Nationals are just now beginning to feel the monumental effects Werth's contract will have on them in the years to come. Werth made $13 million last year. That isn't chump change by any means, but a number paling in comparison to what's coming. He'll make $16 million this year, $20 million in 2014 and then $21 million each year from 2015-17.
With all that money tied into Werth, the Nats didn't land a big bat from the outside this offseason, so they'll be counting on internal offensive improvements to carry them into contention in a loaded NL East.
Washington sorely needs Werth to start living up to the size of his contract. He definitely didn't do that in 2011, batting a mere .232 with a .389 slugging percentage. Werth did not prove his worth, and the onus will be on him to turn it around this year.
Beyond the offensive side of the equation, there will also be some defensive demands that will come when Bryce Harper makes what seems his inevitable Major League debut this summer. Harper's arrival in right, though he played center field on Wednesday, would signal a shift to center for Werth.
All told, the prospects for an already intriguing team become even more promising if Werth delivers.
"Last year was just a bad season," Werth said. "Whatever. I'm over it. I'm ready to play ball, play 162 games."
Anthony Castrovince is a reporter for MLB.com. Read his columns and his blog, CastroTurf, and follow him on Twitter at @Castrovince. MLB.com reporters Joe Frisaro, Ian Browne, Scott Merkin, Bill Chastain and Bill Ladson contributed to this report. This story was not subject to the approval of Major League Baseball or its clubs.