While the Mariners won’t officially confirm the news until later today, Jesus Montero is currently on waivers, free to any team who wants to pay the $20,000 waiver fee and is willing to put Montero on their roster. This is quite the downfall for a guy who, not that long ago, was drawing comparisons to some of the best hitters in baseball.

“In terms of hitting ability, Montero can be a Manny Ramirez or a Miguel Cabrera,” [New York Yankees general manager Brian] Cashman told ESPN New York’s Ian O’Connor. “As a catcher, he’s got a cannon for an arm. As far as everything and what I want him to be, I want him to be Jorge Posada.” Cashman added, “He has a chance to bat third or fourth. He has the potential to be a beast in the middle of our lineup.”

And before you start thinking that Cashman was simply participating in the Yankee-prospect hype machine, this is what he said about him after he traded him to Seattle for Michael Pineda.

In a tweet Friday night, Bergen Record columnist Bob Klapisch quoted Yankees general manager Brian Cashman saying, “To me, Montero is Mike Piazza. He’s Miguel Cabrera.”

To this point in his career, Montero has 865 plate appearances and a 92 wRC+, which puts him in the Orlando-to-Asdrubal tier of Cabreras, rather than the Miguel tier for which Cashman hoped. A guy who hits like a shortstop but can’t run or play the field isn’t much of a big leaguer, which is why the Mariners are willing to give Montero away to anyone who wants him. And why Montero serves as a reminder about how little certainty we should have when it comes to forecasting the future performance of hitters.

Many words have been written about the variability of pitching prospects. For a while, statheads even took pride in an acronym suggesting that pitching prospects were a myth, a collection of hopes and dreams that most often resulted in injury and disappointment. But while prospects who hit come with fewer health issues, it’s also quite difficult to identify great hitters before they establish themselves as such in the big leagues. That Montero was identified as one such potentially great hitter and didn’t pan out isn’t a rebuke of the entire attempt to scout hitting talent, but a look at the list of the best hitters in baseball should serve as a reminder about just how challenging it is to see offensive greatness in a young player.

Heading into 2016, Bryce Harper is probably the best hitter alive, and certainly, scouts have seen him coming for a long time; he was on the cover of Sports Illustrated as a 15-year-old. But after that, it gets a bit murky.

Mike Trout was certainly highly regarded, and was taken in the first round of the 2009 draft, but he famously went 25th overall; there are lots of stories about teams who had him very high on their draft boards, but it’s fair to say that no one saw this coming. Trout has become the Mickey Mantle of his generation, vastly exceeding what anyone thought he would be. And yet, even the fact that he was a first-round pick makes him somewhat rare among the game’s best hitters.

Giancarlo Stanton, the game’s most prodigious power hitter? A second-round pick in 2007. Joey Votto, who has the 15th-best wRC+ in baseball history? Second-round pick. Paul Goldschmidt? Eighth round, and never appeared on Baseball America’s list of the top 100 prospects as he climbed the minor league ladder.

These are the best hitters of their time, but they weren’t seen as elite talents coming into professional baseball. And plenty of the other best hitters in the game weren’t even considered to be high-end players by the time they reached the big leagues. Jose Bautista, Edwin Encarnacion, Anthony Rizzo, Chris Davis, and Josh Donaldson all passed through multiple organizations, traded because their original clubs weren’t sure what they had on their hands. David Ortiz, of course, was famously cut by the Twins before going to Boston and becoming a franchise icon, and before that, the Mariners traded him to Minnesota for Dave Hollins.

And of course, there are guys like J.D. Martinez, guys who came out of nowhere to turn into offensive monsters. David Peralta also fits that mold, as a converted pitcher who had to lobby for a job while playing in independent ball, and now looks like one of the best right fielders in the game. Matt Carpenter was basically an organization guy when the Cardinals drafted him, then they turned him into an interesting role player to get him to the big leagues, and now he’s a legitimate All-Star with serious power.

Yes, there are guys who were projected as great hitters who have lived up to the billing. Scouts saw Miguel Cabrera as a teenager and identified him as a monster at the plate, and he’s lived up to it. Buster Posey and Manny Machado were high draft picks who have become superstars, and Carlos Correa and Kris Bryant look like they’ll follow in their footsteps. This isn’t all dart-throwing.

But projecting offensive performance from teenagers is just really difficult. Power can be seen, and the lack of power can usually be ascertained with a higher degree of certainty, even with guys like Carpenter or Mookie Betts hanging around as reminders that nothing is written in stone. But the stuff that makes great hitters that isn’t hitting the ball really far; that stuff is really, really difficult to see in advance.

And that stuff was essentially the basis for the rosy projections for Jesus Montero, because he didn’t do anything else at a big league level. He couldn’t run or field, but he was identified as a potential superstar because a lot of very good evaluators were convinced that he had special offensive skills. And you know what? We don’t even know that they were wrong. Maybe Montero really does have those skills, but simply didn’t put in the requisite work in order to develop them properly. Maybe the systemic failures of hitting prospects coming through Seattle damaged Montero’s development, and resulted in something less than what he would have been elsewhere. Maybe he’s still going to become what he was projected to be, and we’re just seeing the beginnings of the next Edwin Encarnacion.

But as Montero sits on waivers, available to anyone for basically nothing, it’s useful to remember just how difficult it is to identify great hitters at a young age. While many talk about the uncertainty surrounding defensive metrics, we should be far more skeptical of overly-certain claims about a young player’s future offense than we should be about whether a big leaguer saved 10 or 20 runs with his glove in a given year. When it comes to young hitters, we still don’t know a lot. No one does, because so much of what makes a great hitter isn’t easily observed in short bursts.

For bat-only prospects like Montero — guys who have to hit in order to have value at the big league level — we should remember that the spread of outcomes is always going to be remarkably high. Accurately projecting the future path of a young hitter is remarkably difficult, and we just don’t know as much about hitting as we do about the other things that a player can do to impact a team on the field. That doesn’t mean Montero wasn’t a real prospect, or that guys like A.J. Reed aren’t also highly valuable assets within an organization, but Montero is a reminder of how far we all still have to go before we can be confident in saying that any prospect has can’t-miss offensive ability. Often, they do indeed miss.