It is one of the most frequently asked questions among Angels fans during a tumultuous offseason that has brought profound change to the roster and internal dynamics of the three-time defending American League West champions.
The language barrier was about the only hurdle he didn't conquer after arriving from Montreal in 2004 and winning the AL Most Valuable Player Award in his first season as manager Mike Scioscia's new right fielder.
Guerrero's passion for the game and all-out style, coupled with seven seasons spent on the most horrific of the sport's artificial surfaces in Montreal, have conspired to rob him of his former speed and explosiveness on the bases and in the field.
A succession of injuries having taken a toll -- it was sad to watch him struggle to get through 100 games last season, reduced to only two starts in the outfield.
After 12 consecutive seasons hitting at least .300 and 11 straight 25-homer-or-more seasons, Guerrero slipped to .295 and 15 home runs in 2009. He began the season recovering from knee surgery and went on the DL twice, with a torn pectoral muscle and a leg ailment.
In the final year of his contract, Guerrero's timing couldn't have been worse. A man who'd been one of the game's premier players for so long suddenly produced more question marks than exclamation points at age 34.
The Angels concluded that Bobby Abreu -- who performed so brilliantly in 2009 as the free-agent bargain of the season -- was a better fit in right field.
Abreu was signed to a two-year deal with an option for a third. The decision was made that another left-handed bat with power and discipline was a bigger need in a lineup tilting toward the right side, and Matsui was the choice.
"He's a veteran hitter," Angels manager Mike Scioscia said of Matsui, who arrived with a bang in the Bronx in 2003 after a storied career in Japan. "He has the ability to hit in the middle of a lineup and be a very, very good run producer. His plate discipline is also important to, I think, any club.
"I think Hideki is a unique talent that obviously overcame some injuries early to have an incredible  season. And I think we saw what he did in the playoffs, and I think it's indicative of his talent."
The $6.25 million deal plus incentives the Angels made with Matsui is similar to the one they extended Abreu the previous winter. It came to $6 million with bonuses reached. Abreu is returning for $19 million guaranteed for two seasons, plus a third year for $9 million based on plate appearances. It's a reasonable figure for such a productive player.
In style and approach, Matsui is much closer to Abreu than Guerrero. Like his former teammate with the Yankees, the man from Japan is a patient, disciplined hitter with a .370 career on-base percentage. It has held steady at .367, .370 and .367 the past three seasons.
Guerrero's career on-base percentage is higher than Matsui's at .386, but it is in free fall. He has been sliding the past three seasons, from .403 to .365 to .334.
Once one of the game's most feared power hitters, Guerrero has had 27, 27 and 15 homers the past three seasons. Matsui has produced 25, 9 and 28.
Matsui will miss Yankee Stadium's cozy right-field dimensions when he settles in at Angel Stadium, and he figures to land somewhere in the 20-homer range. But if he hits around .292, his career average, with a .370 on-base percentage, he'll be highly productive in a deep lineup.
Then there is the matter of postseason play.
Matsui is the reigning World Series MVP. He earned that distinction while starting only three of the six games against the Phillies, losing his DH spot in the National League park.
Matsui's performance in the deciding Game 6, complete with a homer and six RBIs, is the stuff of Yankees lore.
In 56 career postseason games, Matsui has been even more lethal than in the regular season, batting .312 with a .541 slugging percentage (compared to .482 in the regular season) and a .391 on-base percentage.
Matsui has produced 10 homers and 39 RBIs on the biggest stage.
Guerrero had his first exceptional postseason performance in October, leading the club with his .378 average in nine games, with three doubles, a homer and seven RBIs.
In 29 career postseason appearances, Guerrero is hitting .286 with a .365 on-base percentage and .375 slugging mark. He has two homers and 14 RBIs.
Matsui, who turns 36 on June 12, is a year and four months older than Guerrero.
Lyle Spencer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.Less