If you’re a Yankee fan and you’re looking for a good reason for why your team dropped two of three to that other local baseball club, it may be that the three one-run games the Yankees played at Shea Stadium, two of which ended in losses, is as simple as the absence of Jorge Posada. After all, Posada was a great hitter on a hot streak, the saving grace of a lineup missing two of its greatest run producers. When back spasms forced him to exit from the first game of the series, it might have been the straw that broke the attack’s back.

In truth, the root cause of those two losses, not to mention the sole, narrowly won victory – a gift from Billy Wagner, who may never again have an inning so bad – lies in the team’s complacent winter. Sure, the Yankees saw to the big-ticket item: repairing a center field position that was bleeding outs on both offense and defense with the acquisition of Johnny Damon. But smaller, albeit no less significant holes went unaddressed.

Second-line depth has been a problem for the Yankees for years, and they have been strangely resistant to learning the lessons of their own recent history. The Yankees will spend millions on starters but pinch pennies when it comes to buying reserves. This has been an issue at least as far back as November 3, 2001, when a profound lack of foresight found the team in a World Series against a then-potent Randy Johnson with no strong righty hitters in reserve. The words, “Luis Sojo, 1B,” can be found in the box score for that day, a foreshadowing of the “Miguel Cairo, 1B” entries of today’s Yankees lineups.

The Yankees didn’t win that World Series and they haven’t won one since. The lack of championships and the rise of “Luis Sojo, 1B”-style reserves are not coincidental. Think back to 1998, when Sojo was an afterthought among a cadre of reserves that included, at various times, Darryl Strawberry, Tim Raines, Chad Curtis, Shane Spencer, Ricky Ledee, and Homer Bush. Confronted with an injury, the Yankees had an answer. If a pinch-runner was needed, if a lefty reliever came in, if a righty reliever was in the game and they needed a home run to win, the Yankees had options.

Of course, 1998 was a special season – if that season’s epic home run chase has since been diminished by rumors of steroid use, the Yankees’ historic season remains – and it is virtually impossible to maintain such a good bench from year to year even if you try. But the Yankees haven’t tried. If anything, they’ve gone in the opposite direction. Even in the face of the dramatic 2004 playoff loss to the Red Sox, keyed by reserve specialist Dave Roberts’s clutch stolen base, the Yankees have refused to stock their bench with adequate emergency parts.

Roberts was a reserve outfielder, an area which the Yankees refused to address this past off-season despite glaring weaknesses. As durable as Hideki Matsui, Johnny Damon, and Gary Sheffield had been in recent seasons, injuries are by their nature unpredictable; just because Matsui had proved to have an iron constitution did not inure him to broken bones, or, for that matter, being hit by a car. Within two years prospects like Brett Gardner, Jose Tabata, and Austin Jackson may give the Yankees a trio of high quality replacements for their aging veterans, but the upper-levels were completely without viable substitutes, young or otherwise.

In the off-season a number of versatile outfield reserves changed hands. Putting aside expensive and questionable starters such as Juan Pierre and Milton Bradley, trades included Termel Sledge (twice),Matt Diaz (.390 AVG/.387 OBA/.644 SLG with the Braves), Rob Mackowiak, Gabe Gross, and Larry Bigbie. Jason Michaels of the Phillies was rumored to be available for months before he finally went to the Indians for Arthur Rhodes. David Dellucci went from the Rangers to the Phillies, where he now rots on the bench. Jeff DaVanon (.298/.375/.464) spent all winter on the free-agent market before the Diamondbacks took pity on him.

The Yankees either stayed out on these players or were ineffective when they went in. Instead, they placed their faith in Bubba Crosby, the unproven 29-year-old, who, in a best-case scenario, would not equal half the production of a Sheffield or Matsui if called upon to play for them. Then, in a fit of rash sentimentality, they re-signed Bernie Williams, which blunted the Damon signing by taking Williams’s wilting bat and shifting it elsewhere rather than replacing it.

This same lackadaisical approach to reserve strength has resulted in Miguel Cairo and arguably Kelly Stinnett, for all the good his special relationship with Randy Johnson has done. It also afflicts the pitching staff, where the team had good reason to believe that Aaron Small and Shawn Chacon might fall into the one-year wonder category, that Jaret Wright might never find his way back, that Carl Pavano might never be healthy. Throughout the off-season, rumors persisted that some of the more credulous general managers in the game were willing to deal for Pavano. If true and the Yankees passed, then their own level of credulity must be redefined, for Pavano was a chimera even before he was signed, and if a solid season of his chronic injury problems didn’t cause the scales to fall from pinstriped eyes, then perhaps those eyes were closed to reality.

Since 1996 the Yankees have been quite lucky in regard to injuries. Derek Jeter missed a quarter of the season in 2003 and yet the Yanks went to the World Series. This taught the team to cheat on depth, to gamble that in case of a serious injury, one expensive starter would take up the slack for another. For most teams, that doesn’t happen; the loss of a star creates a vacuum.

As the old saying goes, nature abhors a vacuum. By the end of the week, the Yankees will have given some indication of whether their inattention to detail will let the Red Sox fill this one.

Mr. Goldman writes the Pinstriped Bible for www.yesnetwork.com and is the author of “Forging Genius,” a biography of Casey Stengel.