Let’s get one thing out of the way up front: I’m not trying to diminish the significance of winning two World Series in three years. It’s a tremendous achievement.

But when you try to process how the San Francisco Giants went from that to what they are now — dead last in the NL West — it’s important to understand that the Giants haven’t fallen as far as your typical World Series champion would.

The 2010 Giants won the World Series by bulldozing two of recent baseball history’s juggernauts — the Phillies and Rangers — in the playoffs. General manager Brian Sabean and manager Bruce Bochy cobbled together a lineup that was five years past its expiration date — Juan Uribe, Pat Burrell, and Edgar Renteria had all seen better days — and got hits in key situations from the likes of Cody Ross. And credit to them for that. Before the Giants got to them, Cliff Lee had practically never given up a hit in the postseason and Roy Halladay had literally never given up a hit in the postseason. Bochy was aggressive with his starting pitchers, and they rewarded him with superb performances.

The recipe for 2012 was similar — great pitching and good enough offense, en route to a lopsided World Series victory over a team that looked quite formidable on paper.

But the dirty secret of the playoffs — particularly in baseball, but in all sports — is that the best team doesn’t always win in a short series, especially when the so-called underdog can take advantage of the outsize effect that starting pitching has in the postseason. San Francisco in recent years has been like the Fray’s first hit single — home not only to cable cars, but to a team that everyone knows was playing a little over its head.

Which is not to say the Giants weren’t good last year, or that they weren’t well suited to make a run in the playoffs. They were excellent, boasting an underrated lineup, generally solid defense, and one of the deepest pitching staffs in the game. But they also won 94 games against a Pythagorean record (using run differential to predict a win-loss record, mitigating the effect of things like record in close games) of 88-74. Look beneath the surface and you start to see other anomalies: Angel Pagan, who’d been about a league-average hitter over six seasons as largely a part-time player, had an outstanding season, collecting 61 extra-base hits and hitting .288/.338/.440. Minor league journeyman Ryan Vogelsong continued his two-year renaissance, and Barry Zito, despite all the grumbling about his contract, was hardly disastrous in 184⅓ regular-season innings, and was then spectacular in his final two postseason starts. And whatever normative stance you want to take on Melky Cabrera, and whatever you want to attribute his pre-suspension numbers to, the Giants still banked 113 games of .346/.390/.516 production from their left fielder, 4.7 wins above replacement, according to Baseball-Reference.

Those things have all fallen through this season. Cabrera’s not only ineffective but gone. Zito’s ERA has climbed by more than a run compared with last year. Vogelsong’s been injured, which is just as well, because his ERA is up 3.34 runs — it’s almost exactly doubled. Pagan was back to being an average hitter (100 OPS+) before sitting down with hamstring problems. And when you add Jeff Francoeur to your starting lineup, you’re just asking for trouble.

Apart from that, little things have hurt the Giants. World Series hero Pablo Sandoval has gone in the tank this season, shedding 100 points of OPS and looking and moving like he ate them. Matt Cain’s collapse hasn’t actually been as bad as it looks — despite adding a run and a half to his ERA, his FIP is only up about half a run. Even Buster Posey’s production has dipped slightly, which seems kind of churlish to point out, considering that his OPS+ has only “dropped” to 149 this season and he still plays baseball like he’s two or three evolutionary steps ahead of his contemporaries.

Even with surprising years from the middle infield tandem of Marco Scutaro and Brandon Crawford, the Giants are 12 games worse than they were this time last season. And while this team was among the league’s best when everything was going well, an almost complete reversal of fortune has turned largely the same roster into one of the league’s worst.

As if all the internal instances of wheels falling off (or going off the rails, or crashing and burning, or whatever transportation-related disaster metaphor you prefer) weren’t bad enough, external forces haven’t been kind to the Giants in 2013 either. You see, in 2010 and 2012, the Giants were the best of a truly dire National League West. In 2010, they caught (at the very last moment) a pretty mediocre Padres team, while in 2012, they ran away from a division in which their closest competition was a foundering Dodgers team that might as well have been governed by S.R. Hadden’s first rule of government spending: “Why have one when you can have two at twice the price?”

A year later, the Dodgers seem to have finally put things together, disappearing over the horizon, looking like the NL West’s first regular-season juggernaut in a decade. It’s easier to win your division when you’re the only team that has a clue. It’s tougher when your most heated rival, well, suddenly turns into the 1951 Giants.

It seems obvious that if a team goes from the World Series to last place within 12 months, there’d be a good reason, some catastrophic injury or alien abduction that robs the team of its star. Or some shortsighted front office foolishness such as has sunk the Phillies and Yankees this season. Not so in San Francisco.

I wish there were some greater meaning to the Giants’ disappointing season, some lesson to be taken from what must be a painful letdown for fans so used to success of late. In the absence of that, Giants fans can be comforted by the presence of some very good pitchers and one of the few true franchise cornerstone players in the game right now. And the fact that if as many things go right next year as went wrong this year, next August will look a whole lot better.