The primary job description of a baseball general manager is to build a franchise that can compete year after year. You build a system of young talent, you supplement it with veterans, you sign your most promising players to long-term deals, you placate the media every couple of weeks or so. It's a tough job, but its primary parameters are simple. The timeframe, in general, is eternity: The goal is to win forever.

That might be the most important part of being a general manager, but it's not the hardest one. The hardest one is knowing when to step on the gas and when to let off. I think I'd enjoy being a general manager from August to June. But I think I'd hate it in July.

(Warning: Cardinals column coming.)

The Cardinals' John Mozeliak is one of the best GMs in baseball. He helped shepherd (along with current Houston GM Jeff Luhnow) one of the best farm systems in the game. His free agent signings are surgical and precise; he's one of few GMs who tends to get his money's worth on the open market (Matt Holliday, Carlos Beltran, Lance Berkman, Jhonny Peralta). He had the self-assurance and intestinal fortitude to say goodbye to a franchise legend in Albert Pujols, a move that now looks like it might have saved the whole organization. The guy knows what he's doing.

But he's faced with a decision in the next eight days that will either undo almost everything he's accomplished in his seven years on the job … or further burnish his pristine reputation. He has to decide whether or not to trade Oscar Taveras.

Oscar Taveras, until this year, was considered the best-hitting prospect in baseball. Baseball America compared him to Vladimir Guerrero; Mozeliak himself said he was the best hitter the Cardinals have had in their system since Pujols. There isn't a single person in the sport who has seen him hit who doesn't think he's going to be launching baseballs deep into the night for the next decade. He has a violent, terrifying swing that reminds one of Gary Sheffield's; he's one of those guys you pitch to, and duck.

Here's a video of his first major league home run:

There's just one problem with that homer from Taveras: It is the only one he has hit. He launched that one against Yusmeiro Petit, and that has been it. The 22 year-old outfielder is only hitting .200 on the season, and he has a 7-to-2 K/BB ratio. The Cardinals lineup has struggled most of this season, and the spark he was expected to provide has not arrived.

This shouldn't be much of a problem. Taveras is currently the second-youngest player in the National League -- behind Bryce Harper, absurdly -- and is going through the normal adjustment curve for a young player. Even the young stars who exploded out of the gates this year have cooled; Gregory Polanco is down to a .253 average, and Xander Bogaerts has been a disaster. No one thinks those players are somehow flops. They're going to hit, and they're going to hit a ton. Remember: Mike Trout hit .220 in his first 40 games. Oscar is going to be fine.

Unfortunately for Oscar -- and, specifically, unfortunately for Mozeliak -- Oscar's struggles are coming while two other things are happening. The first is that Cardinals manager Mike Matheny is, in his third year, still going through a learning curve, and he may be regressing. One of Matheny's major attributes as an unproven manager was his ability to trust and connect with young players; it was touted as an antidote to the Aaron Miles obsession that seemed to plague Tony La Russa. (Though it's worth noting that the Cardinals' last two World Series were won when TLR put his faith in young guys during the postseason.) But this has fallen away in his third season. Matheny has turned into a crusty old salt, letting hitters like Mark Ellis, Allen Craig and Daniel Descalso flail away while young players like Taveras and, until recently, Kolten Wong sit the bench. Craig is having a nightmare season, but Matheny keeps sending him out there while Taveras -- who, more than anything, needs reps -- sneaks in for a pinch-hit appearance occasionally. It is making Taveras look like a disappointment … expendable.

The other thing conspiring against Taveras is that David Price is available on the trade market. Price is having another outstanding season, and even though the Rays have won six in a row, they're still highly unlikely to make the playoffs (at 9.5 percent playoff odds according to Baseball Prospectus) and really only have this last trade deadline to maximize any return they'll get for him, considering his contract expires after next season. Price has shown a little leg -- even doing the wave at Busch Stadium during an off day last weekend -- and it's clear he'd be a fit in St. Louis this year, next year, many years afterward. And considering the Cardinals' rotation question marks and a tight NL Central, St. Louis could certainly use him.

But these are the Rays, who two years ago got Wil Myers (a worse hitter to Taveras) for James Shields (a worse pitcher than Price). They are highly skilled at this trading-for-prospects game; it is a foundation of the franchise's entire business plan. If they are going to trade Price -- a guy they've arguably been trying to trade for two years now -- they are going to raid the fridge. They are going to want everything. They are going to want Taveras.

Believe me, I've looked through the Cardinals' treasure trove of prospects and tried to talk myself into the Rays taking guys other than Taveras. Shelby Miller, Stephen Piscotty and Randal Grichuk? Not gonna do it. Carlos Martinez thrown in? Still probably no. The Rays will not do this trade without Taveras, particularly in a world where the A's will trade superstar prospect Addison Russell for two Cubs pitchers dramatically inferior to Price. If the Cardinals want David Price, it'll cost them Taveras. And probably more.

So, we come back to Mozeliak. Every team in the pennant chase in late July has to run decisions through this calculus: Is having a better chance at winning this year worth having less of a chance of winning in the future? And how much better is that chance? The Cardinals need to stave off the rest of the division -- and by "stave off," I mean, "actually get into first place;" they're a game-and-a-half back right now -- and Price gives them the best chance to do so, not to mention given them a glimpse of what an Adam Wainwright-Price-Lance Lynn-Michael Wacha (maybe) postseason rotation might look like. Price must look so tempting.

But he is a pitcher, one who is about to become insanely expensive. (Three of the 10 highest-paid pitchers in baseball are currently on the DL, and two others -- Matt Cain and Justin Verlander -- are clearly ailing.) Long-term pitcher contracts rarely work out, particularly guys like Price, with unconventional motions and high velocity. Barring a freak injury, Taveras will be nearing the peak of his ability in four years; can we say the same thing about Price? Acting like Price is a sure thing but Taveras is the risk is backwards.

Even though the Cardinals aren't in first place, they're still favorites to win that division (44 percent, says B-Pro, ahead of Milwaukee's 31 percent, Pittsburgh's 16 percent and Cincinnati's 8 percent). That's if they don't make a single move, if they just keep going as they have been. And as pretty as the aforementioned postseason rotation sounds, the team with the best rotation doesn't usually win the World Series. (The last time that happened was probably 2001, which is the year everyone always thinks of when they try to stack postseason rotations.) Weird things happen in the playoffs. The Red Sox won in 2013 because David Ortiz went insane. The Giants won in 2012 because the Tigers never showed. The Cardinals won in 2011 because the universe collapsed in upon itself. The Giants won in 2010 because of Aubrey Huff and other castoffs. Once the playoffs begin, all bets are off. It's madness, chaos.

Thus the goal should be not to wager everything -- the future, cost control, violent awesome uppercut swings -- on one season and instead try to make sure you make as many postseasons as possible. Making the postseason is great this year; making it every year for the next five -- which Taveras at a low salary is FAR more likely to help the Cardinals do than Price at a massive one -- is the point of the job.

But it's easy for me to say that. It's tougher for Mozeliak, who's facing a manager afraid to play a rookie, an All-Star openly salivating about playing for a contending team, a tight pennant chase and a Rays front office renowned for its poker face. Thus, we get back to what a general manager's job is. Is it to maximize winning this year, even if it's just an incremental uptick in odds? Or is it to stay the course and make sure you're back next year, and the year after that?

I think it's the latter. I think guys like Taveras come around too rarely. I think if the Rays want Taveras, Mozeliak should walk away, no matter how much it hurts, no matter how enticing Price is. But I'm not the one in charge. This month, jeez, who would want to be?

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Email me at leitch@sportsonearth.com; follow me @williamfleitch; or just shout out your window real loud, I'll hear you. Point is, let's talk.