In his novel “Mother Night,” the late Kurt Vonnegut laid out this maxim: “We are what we pretend to be, so we must be careful about what we pretend to be.” The Yankees have been pretending to be a losing team for nearly a quarter of the season, and it’s worth asking whether they are now what they appear to be.

After the team’s most recent loss, a lethargic 5–3 defeat at the hands of Chicago’s rookie lefty John Danks in the first game of yesterday’s doubleheader, the Yankees’ record is 17–20. Analysis conducted by an author of Baseball Prospectus, Rany Jazayerli, has shown that a team’s record at the 30-game mark is often a firm predictor of the rest of the team’s season. If you haven’t figured out how to get it right one-fifth of the way into the season then it’s very likely you’re not going to figure it out. Similarly, if you’ve had a streak of bad luck you might not have good luck again until next April (or, as was the case with the Yankees of the 1980s, who just needed one free-agent starting pitcher and one shortstop to work out, you might not find it for 15 years).

Of course, all teams are different. Many teams that start a season with losing records deserve them. The 1962 Mets were 12–28 at the 40-game mark because they were a poorly equipped expansion team. Roger Clemens was not going to pitch for them in June. Phil Hughes was not going to come off the disabled list and go 10–0. Tom Seaver was still in high school. If a team with this kind of record doesn’t turn its season around and go on to the World Series, it’s because it had no chance of doing so in the first place.

Still, there have been teams that had the potential to be good that fell victim to bad luck or injuries or an unexpected decline in performance by a star player or two that never managed to escape the gravitational pull of their losses. The 2005 Yankees, who started out 11–19, managed to pull it off, but such teams are rare. A better analogy to this year’s Yankees may be the 1959 edition, a disappointing unit wedged between four consecutive pennant winners before it (1955–1958) and five consecutive pennant winners after (1960–1964).

It seems unlikely even in retrospect that the 1959 team would have failed to compete, but at the end of May the club was 19–23, in sixth place, and six games behind the leader. They improved thereafter, and got themselves over .500 in June, but consistency eluded them and they quickly suffered a relapse. Mickey Mantle had an off year by his own high standards; first baseman Bill Skowron got hurt and missed the second half of the season; Hank Bauer reached the end of the line, and the starting rotation was a loss after the first two starters, Whitey Ford and Art Ditmar. For the first time in his life, an aging Casey Stengel became complacent and let the club’s problems fester while he napped on the bench.

But those Yankees had a good enough core that things were fixable — they came roaring back the next season. Key word: next season. Even with all the team’s great resources, it was unable to figure out how to arrest the team’s drift. The killing blow was the loss of Skowron. The Yankees were 41–41, 6.5 games behind the firstplace Indians (the White Sox would eventually claim the title) when a bad back knocked the first baseman out for two weeks. The Yankees went 6–7 while he was out. On the day he returned, Skowron stepped into a baserunner as he tried to field an errant throw and had his left arm snapped in two places. Although the Yankees recovered enough to go 31–27 the rest of the way, too many games and too many teams had already come between them and the leaders.

Few had projected anything other than a first-place finish for the Yankees that year, just as few had expected the Yankees to struggle this year. In truth, the team’s problems were foreseeable, if not to their fullest extent. Most who hedged on the Yankees focused on the team’s lack of an ace starter, but Brian Cashman had arranged good pitching depth, something that has only been augmented by the Clemens signing. The real problem was on offense, where it was assumed that good performances by the stars would offset a pathetic bench and the inevitable injuries. But if Mickey Mantle can have an off year, then Bobby Abreu can, too.

History has shown these problems don’t get fixed. The Yankees can do it, but their window for doing so narrows by the game and will soon close.

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