All baseball players age differently. Some of the most important research sabermetric thinkers have churned out over the past 25 years have been about which skills age most and least gracefully; which peak at which times; and at what age players typically peak. However, the caveats attached to those data are critically important, because all of the data that show single curves actually reflect massive smoothing of widely disparate curves. Even similar players learn, adjust and age differently.

Position players, at least, have a curve. Few are linear in their development, but virtually all peak between 26 and 29, and one can more or less sketch out how players (who enter the league with certain batting and defensive skills and at certain ages) will age. For pitchers, there is simply no good data. Some pitchers peak at 23; some peak at 36. Some learn command, or adjust their mechanics, or learn a cutter. Some lose three miles per hour, or leave them on an operating table, and are never again as good as they are in their second or third season.

Because pitcher development is so unpredictable, it’s usually frustrating for fans. Some pitchers get rushed through the minors; miss time during which they might have made certain refinements or changes; and spend years at the big-league level trying to catch up. Others weather overuse at a young age without getting injured, but their performance falls off as a result. Still others take a decade to find whatever weapon or approach it is that maximizes their talent in the big leagues. Fans tend not to see all this, and even those who do sometimes fall victim to prejudices of performance.

I’m talking, in a passive voice and a too-passive style, about Edwin Jackson. He signed a four-year, $52-million deal with the Chicago Cubs the week before Christmas, and since then, I have read a dozen or more distinct stances on the decision. No one seems to object to the money on its own grounds. The disagreement seems to be between those who like Jackson and think he can turn the corner; those who think he already HAS subtly turned said corner; and those who mistrust him based on past performance and teams’ unwillingness to commit to him until now.

I believe it’s one of the first two. I think, like many hurlers before him, Jackson is paying for the crime of not having developed on the schedule set for him by fans, and that although his cleats may be left in the hardened concrete of the baseball world’s hastily-formed opinions, Jackson has found his stride and will hit the ground running in Chicago.

Before I get really into the psychology of fan opinion, I want to defend my position on Jackson specifically. As it turns out, ‘hit the ground running’ is a pretty good segue on that score.

The most important thing Edwin Jackson has learned in recent years (and he HAS learned, and grown, as evidenced by a career-best strikeout rate and strikeout-to-walk ratio in 2012) is how to bury his slider.

I do mean bury. I went back through video archives on the Washington Nationals’ web site, and a simply stunning number of Jackson’s strikeouts last season came on sliders down, often in the dirt and requiring a throw down to first base. Indeed, per Mark Simon of ESPN Stats & Info, Jackson had the league’s best swinging-strike rate on sliders last season. It was 49 percent. Batters missed very nearly as often as they connected when swinging at Jackson’s slider last year. As a result, Jackson saw his overall swinging-strike rate rise to a career-high 12.2 percent.

Of course, there is a real problem. Jackson’s fastball is not missing bats. Although he sits comfortably around 94-95 miles per hour with it and can touch 97, it has simply never been a pitch with enough command or movement to get by batters as often as a fastball that hard ought to do. Refer again to the ESPN article linked above to see specifically what problems Jackson had over the second half of last year when elevating his heat. It’s fairly intuitive, though. The straightness of his fastball makes it necessary that Jackson keep the ball down, other than an occasional high heater at an unexpected moment, and then only to change the batter’s eye level.

That leads me into another thing to like about Jackson, which is that he really DOES keep the ball down. Over the last three seasons, his ground-ball rates have been 49.4 percent, 43.8 percent and 47.3 percent, respectively. When he locates the fastball near the bottom of the zone, he becomes unhittable, not only because batters might chop the ball into the ground on those occasions, but because his slider (which can touch 90, but sits around 87, and has a mostly downward snap) looks so much like the fastball out of his hand that batters have a tough time laying off of it.

One can’t help but wonder whether Jackson, who lost about 1.5 miles per hour on all his pitches’ average velocities in 2012 from their previous heights, might be disproportionately hurt by any continued drop. How much slower can the fastball get before batters feel less compelled to gear up for it and learn to let the sliders skip by uninterrupted?

Still, it seems that Jackson has never had a better idea of how to truly use his stuff than he does now, and he’s also a durable arm.

It’s time to address exactly what it is that makes fans, and seemingly even some teams, so mistrust Jackson. It actually has a little bit to do with the last line of the preceding paragraph, so let me start there: Fans will forgive pitcher injuries, at least once or twice. Far less tolerable for them, though by far preferable for both the hurler and his team, is for a pitcher with apparent upside to pitch only fairly well, or Heaven forbid, poorly, on any sort of regular basis. Rick Porcello suffers from Jackson’s disease for the same reason. In terms of popularity, and maybe even job security, it would have behooved Jackson (called to the big leagues by the Dodgers at age 19) to overthrow, flash brilliant strikeout stuff and miss huge chunks of six seasons in his 20s, rather than pitch at only moderate effectiveness and remain healthy. If you have trouble believing that, I offer as case studies Kerry Wood and Carlos Zambrano, each overused in youth, each inconsistent after age 25, and I ask: Who had a former grip on the hearts of Cubs fans? I think it was very clearly Wood. Yet, who was worth more? It’s closer, but the answer is Zambrano.

For reasons I will never understand, fans seem to prefer “great or hurt” guys to ones who will be on the mound more often but have less upside. Even some teams think this way. Yet, go down any list of recent playoff teams, and count the number of starts lost to injury. Neither the Nationals, nor the Giants nor the Reds lost any last season. The Tigers lost fewer than 10. The 2011 Milwaukee Brewers lost five. The Yankees that season lost fewer than 10. You’d rather have to shuffle guys between Triple-A and MLB, or between the rotation and the bullpen, because you have no clear fifth starter, than give any starting nods to the seventh, eighth, ninth guy on your organizational depth chart.

That’s one issue. Another is that fans are impatient. Perversely, in fact, they’re less patient the better the player they have to wait on could be. Fan opinion solidifies quickly, and is very difficult to change. Actual pitching skills, though, change all the time. That’s what makes pitchers so much less predictable than hitters.

Finally, we return to the fact that Jackson made his debut at age 19. He has been around, believe it or not, as long as Dan Haren (replacing him in Washington) and David DeJesus (Jackson’s new center fielder), and at this point, because fans have seen so much of him without any sign of imminent breakout, no further progress is expected. What fans can’t account enough for, try though they may, is that Jackson is four years DeJesus’s junior, and three years younger than Haren.

Edwin Jackson finally has a chance to settle in somewhere. He will probably be pitching to Welington Castillo for at least the next two years. He gets an opportunity to learn to trust Castillo to get in front of bouncing sliders, and for Castillo to learn how to frame the high fastballs for some key strikes to set the sliders up. He’s an improving pitcher, even as he heads toward 30. Hopefully, he’s in a situation fluid enough (he did sign with a rebuilding club, after all) that he won’t be hemmed in by minds already made up.