There’s an old Warner Bros. cartoon, “Show Biz Bugs,” in which Bugs and Daffy Duck are vaudevillians trying to outdo each other. Daffy finally wins the audience’s affection by blowing himself up. Bugs implores him to do an encore. “That’s terrific, Daffy! They loved it. They want more.”

“I know, I know,” Daffy testily replies as his ghost ascends to Heaven, “but I can only do it once.”

The Yankees are currently exploring what we might call Daffy’s Dilemma: the chance that any performance seen only once or a few times can’t be sustained or repeated. Several hitters have hit the ball out of the park in their first major league at bat. But we don’t assume that he will also hit it out in his second, third, and fourth at bats. Instead, we wait and see what he does in his next 10 — and if we’re smart, his next 100 — before concluding that he’s the new A-Rod. The Yankees are in the same wait-and-see position with three of their young pitchers, Joba Chamberlain, Phil Hughes, and Ian Kennedy. But chances are that the team believes it only has to worry about the latter two. Depending on whether the Yankees end up playing the seven-day or eight-day American League Divisional Series schedule — the team that finishes with the best overall record in the AL will decide — the Yankees will need three or four starters if the series goes the full five games (and they could elect to use four even if they play the longer series). Barring injury, Andy Pettitte and Chien-Ming Wang are a lock for two of the four slots. Roger Clemens’s gusty start against Boston last weekend allayed fears that his elbow would not be up to the task of finishing this one last coda to his career.

That leaves one spot open. After Tuesday night’s strong outing against the Orioles, Mike Mussina will almost certainly be chosen to fill it. The argument for him will be based on two contradictory notions. The first is that his most recent start should count more than his previous five appearances — his “successful” start at Toronto on September 12 being more an example of good luck on balls in play than pitching dominance. The second is that his career record means more than this year’s inconsistent performance. Remember, even before Mussina began his Steve Trout phase on August 16, his ERA for the season was 4.50, or exactly league average, and opponents were hitting .294 AVG /.333 OBA /.455 SLG against him, which is to say that against Mussina, the average hitter turned into something like Jeff Francoeur.

All teams gravitate toward veteran pitchers at playoff time, on the theory that their experience will allow them to transcend the immense pressure of being on the national stage. Actually, with the division series moving to TBS and the lower ratings expectations for these series, we’re talking about a very small fraction of the national stage. But putting that aside, they fear the youngsters can’t handle the big hoedown.

This is, of course, a myth. There is no evidence that younger pitchers can’t handle the postseason. Over the 104 years since the modern postseason began, there are many examples of young pitchers turning in star performances in October, from Cardinals rookie Johnny Beazley beating the Yankees twice in the 1942 World Series, to 20-year-old Fernando Valenzuela beating them in the 1981 World Series. Every player is an individual and reacts to stress differently. No doubt some young pitchers have folded under the pressure — but it’s certain that many veterans have too. Others, perhaps, shrugged off the heat of the spotlight, but failed to pitch well for the usual reasons —they didn’t have the feel of their curveball, or they hung a slider to the wrong hitter, or the wind was blowing out, or any of dozens of other reasons.

Despite this, the onus is always on the youngster, and this may lead the Yankees to start a mediocre veteran over a promising youngster. Ian Kennedy has pitched very well in his three starts, certainly better than Mussina has pitched in most of his. Yes, there is an element of Daffy’s Dilemma here: Kennedy has thrown just 19 innings, and that small a sample is not to be trusted. Compared to Kennedy, Joba Chamberlain has thrown only 18 innings, but those were enough to earn him the crucial role of late-inning bridge to Mariano Rivera. Should he fold in the crunch, should those 18 innings prove to be an unrepeatable Daffy trick, he can do as much damage in one inning as a Kennedy could do in five. Sure, Chamberlain throws 100 miles an hour, but that doesn’t change anything. Throwing hard is no protection from the character flaw of being young.

None of this is to say that the Moose is the wrong choice. On Tuesday he looked terrific, with better velocity than he had shown a month before. He’ll get one more start before the season ends, and if he shows such good stuff again, the Yankees will have an embarrassment of riches in the pitching department, with no bad choices before them. But there should be no rush to judgment, lest the Yankees choose poorly and execute a stunt of their own that can only be done once — losing in the first round of the playoffs.

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