Why do I think that? Pretty simple really - he's always been excellent. Players who are excellent in one league generally are excellent in the next. We expect the best players in the Australian League or the International League or the Dominican Winter League to become the best players in the Major Leagues. The skills that make you good at baseball are the same, pretty much no matter where you play. Sure, there are some skills that aren't rooted out in the minor leagues. Pitchers who mix their pitches well but have mediocre stuff usually don't excel in the majors. Batters who have a specific weakness that minor league pitchers aren't good enough to exploit might be found out. In general though, the best players at a level tend to carry that through to the next level.
Yu Darvish has been, by far, the best pitcher in Japanese baseball. He has five consecutive seasons with an ERA under 2.00, and he seems to be improving. In 2011, as a 24 year old, he set a career best in every potentially important category - no matter what categories it is you find important: innings pitched (232), ERA (1.44), wins (18) , strikeouts (276), K/9 (10.7), BB/9 (1.4), HR/9 (0.2), WHIP (.828)... you don't need me to tell you that these are exceptional numbers.
It's not just numbers - Darvish has the sort of stuff that, even if he'd had no history of success, would make scouts take notice. Jonah Keri posted this piece on Grantland.com which I can't really add much to. I'm not sure he'll actually throw six pitches - unless all six are excellent, Mike Maddux will probably have him focus on his four best, and perhaps using a fifth on rare occasions. He's also built like the prototypical starting pitcher, at 6'5", 220. If a guy had put those numbers against college-level talent, with the stuff and build Darvish has, they'd probably be the #1 pick in any draft and expected to rocket through the minor leagues.
With that in mind, why does everyone seem so worried?
I know, I know. Daisuke Matsuzaka. Five years ago, he came in with similarly unbridled expectations. He'd been the Greatest Japanese Pitcher Ever. A national treasure. The scouts and stats both loved him - Baseball America named him the #1 prospect in baseball going into the 2007 season. (Go back and look at this list - only five years later, and the list would be... quite different. Anyhow, moving on). It didn't quite work out. His first two seasons were probably better than you remember,* but classifying Matsuzaka's stateside performance as a disappointment is probably fair.
*He was 33-15, ERA+ of 126 in 372.1 innings, striking out 355 and walking 174. Really.
We see tons of comparisons between Matsuzaka and Darvish, some well done, and some less so. Occasionally, I will see these comparisons labeled "racist." I don't think that's fair - Darvish and Matsuzaka were coming from pretty similar circumstances, and begin their U.S. careers at about the same age (Matsuzaka was about 8 months older in April '07 than Darvish will be on opening day). And both came in with similar hype. Certainly some of the people comparing the two are racist, or at least a bit jingoist. Most people, though, are just baseball fans who are trying to get a handle on what Darvish's statistics actually mean. "He was the best pitcher in Japan? So what - we heard all these things five years ago." That's understandable.
So if we're going to compare them, we need to dig a little bit deeper than "the best pitcher in the Japanese League." Both of them being the "best" at their time doesn't make them equivalent, in the same way Pedro Martinez's Cy Young-winning 1999 season wasn't equivalent to Felix Hernandez's 2010. In his last five seasons in Japan, Darvish has a 1.74 ERA and a 4.9 K/BB ratio, while Matsuzaka had a 2.63 ERA and a 4.2 K/BB. Darvish has the superior stuff and build. And, perhaps most importantly, Darvish has the less-checkered injury history - after throwing 240 innings as a 20 year old in 2001, Matsuzaka got hurt and got to only 73 the next year. He didn't reach 200 innings again until the 2005 season. Darvish, by comparison, has thrown 200 innings in four of the past five years, and the one he missed he got to 182. He's thrown more innings, but he's been much more consistent with the innings thrown. All pitchers are injury risks, but a 25 year old without a history of health problems is a better bet than a 25 with a history.
All of which is to say, Darvish should be rated more highly than Matsuzaka was going into 2007.
Beyond thinking he will succeed, though, I need to disclose something to you, the reader. I am rooting, openly, for Yu Darvish to succeed.
Why? Well, for one thing, because I can.
More importantly, I'm rooting for Yu Darvish to succeed, because I want to get over the "can Japanese pitchers succeed in the majors" question. Of course they can. Hideo Nomo, Kaz Sasaki, Hideki Kuroda, Takashi Saito, Shigetoshi Hasegawa, and yes, to an extent, even Daisuke Matsuzaka had success in the majors. None of them had awesome success, though. Of that group, Nomo had by far the most decorated career, winning the 1995 NL Rookie of the Year Award, pitching two no-hitters, and twice leading his league in strikeouts (1995 and 2001). He won 123 games. That's a nice career and all, but no Japanese pitcher was so good that he has taken away the curiosity effect.
*Note: I know that Darvish is half Iranian. That's not especially
relevant - he is, and will almost definitely continue to be, discussed
as a "Japanese pitcher."
What do I mean by "curiosity effect?" Basically, the fact that he's Japanese will be treated as a story itself. When Ichiro Suzuki leads off a game against Darvish for the first time (likely during that April 9-12 series in Texas), inevitably it will be treated as a big deal. In 2012, 17 years after Nomomania, that's a little silly. We don't see that when Carlos Ruiz bats against Mariano Rivera (they're Panamanian!) or Jacoby Ellsbury against Jeremy Guthrie (they're Oregonian!), and I'd like to see a Darvish-Ichiro at bat to be treated as a baseball matchup, rather than a national one.
To create that normalcy, Yu Darvish needs to live up to his lofty expectations. If he doesn't, people will ask why, and the easy answer will be that he wasn't properly prepared to play in the major leagues. Not because he's Japanese, but because they just develop players "differently" in Japan.
However, if he DOES live up to those expectations, and becomes an ace quality pitcher? That's one less question GMs will need to ask themselves, one less question every Japanese pitcher will be faced with, and one more pool of talent that every team will make sure they have access to. That way, when the next phenom comes down the road, instead of "can he pitch in America?" the question will simply be "can he pitch?"