Before Thursday afternoon’s NBA trade deadline, the Cavaliers would like to add a rotation player or three. The Celtics want another scorer. The Rockets and Raptors do too. And why wouldn’t they? Outside of signing a bought-out veteran, this is the last chance for contenders to round out their rosters and refine their approaches to topple Golden State this spring.

Those challengers are all operating under the same, optimistic assumptions: that the hole on their roster is fixable and that an upgrade will meaningfully raise their playoff ceiling. The trade deadline might involve contradictory rumors and complicated pick protections and hectic chatter on Thursday afternoon, but its promise is built on the foundation of hope.

The theory coheres, but in practice, teams that survive into June don’t tend to need a February trade boost. League history has supplied a few go-to examples of immediately transformative midseason additions—Rasheed Wallace in Detroit in 2004, Clyde Drexler in Houston in 1995, Dikembe Mutombo in all his finger-wagging glory in Philly in 2001—but those cases represent the exception rather than the norm. The trade deadline, like life, is largely full of sound and fury, signifying nothing.

Consider, for instance, the most recent teams that have reached the Finals, none of whom made noteworthy midseason deals in advance of their playoff runs. The Warriors have not completed a single such trade with Steve Kerr as coach. Miami’s only in-season additions via trade when LeBron James was in town were bit player Toney Douglas and the rights to Ricky Sanchez. The Spurs didn’t trade for anyone in their 2013 Finals season and only the little-used Austin Daye in advance of their championship the next year.

Those recent teams form the latest points in a long-running pattern. Going back 30 years, less than half of the league’s finalists (26 of 60) have added even one player on an in-season trade at any point, at the deadline or earlier. And because most of those teams added players who either never appeared for them (like Sanchez) or rarely did so (like Daye), that proportion falls even further when limiting the results to only trade targets who actually, tangibly aided their new teams’ playoff runs.

Just 15 percent of finalists in the past 30 years (nine of 60) have added a player on an in-season trade who played in at least 20 minutes per playoff game. Here’s the entire list of those teams and their acquisitions:

2015 Cavaliers: Timofey Mozgov, Iman Shumpert, J.R. Smith

2009 Magic: Rafer Alston

2008 Lakers: Pau Gasol

2005 Spurs: Nazr Mohammed

2004 Pistons: Rasheed Wallace

2001 76ers: Dikembe Mutombo

1995 Rockets: Clyde Drexler

1994 Knicks: Derek Harper

1989 Pistons: Mark Aguirre

Only four of those nine teams won their championship series, the most recent being the 2005 Spurs, who won their title so long ago that James hadn’t even reached the playoffs yet. In other words, only four times in the past 30 years has the eventual champion added an impact player via midseason trade. It seems that even requiring a roster upgrade is, itself, disqualifying for potential title winners, and that (with few exceptions) a champion needs its rotation fully accounted for before a season begins.

This finding not only deflates the perception that February trades matter in the championship race, but it also runs counter to the trend in other sports, like baseball, where transactional activity often affects a given season’s title pursuit. For a variety of factors, ranging from the sport’s more segmented roster composition to MLB’s lack of a salary cap, baseball’s trade deadline produces far more “Rasheed to the Pistons” examples than the actual sport in which Rasheed went to the Pistons. More impact players have been traded to World Series winners in the past three years than to NBA Finals winners in the past three decades: The 2017 Astros traded for Justin Verlander, the 2016 Cubs for Aroldis Chapman and Mike Montgomery, and the 2015 Royals for Ben Zobrist and Johnny Cueto.

Of course, the midseason-trade market generates longer-term ripples—see: Isaiah Thomas’s trade to Boston leading, eventually, to the Kyrie Irving trade—and teams pursue deadline deals for a variety of reasons other than immediate contention. Maybe, like with Stan Van Gundy in Detroit, an executive is trying to save his job with a playoff push, even at a low seed that doesn’t portend a Finals trip; maybe a team wants to clear cap space for the upcoming summer or nab a disgruntled, available star; maybe a front office wants to reshuffle a stagnant and ceilinged roster.

But with many February additions, it’s easy to identify a Finals dream, quixotic though it may be, as the impetus, which means most of these trades fail to achieve their desired goal. Just look at last year: Bojan Bogdanovic didn’t shoot the Wizards into June, nor did Lou Williams for the Rockets; Taj Gibson and Doug McDermott couldn’t help Russell Westbrook win a playoff series; P.J. Tucker and Serge Ibaka couldn’t escape the second round in Toronto. The teams that made those trades were too far away from Cleveland and Golden State for one or two new role players to close that gap, meaning they lost a handful of first-round picks for illusory gains. Now, of those half-dozen players, only Ibaka, who re-signed with the Raptors in free agency, remains with the team that dealt for him.

In the short term, rentals almost never meet their intended purpose, midseason movers rarely swing playoff odds a substantial amount, and purchasing teams seldom capitalize with a Finals appearance. Over the next day and a half, buyer beware.

An earlier version of this piece included Latrell Sprewell’s move to the Knicks in 1999 as an in-season trade. Because of the lockout that year, Sprewell’s move came before the season began.