Welcome to the mystery of sports psychology, the enigma that is Seton Hall’s basketball team.

Unbeatable before the calendar turned to 1999, unimpressive since then. Undefeated at home, uninspiring on the road. For a number of reasons, the Pirates have proven to be one of the biggest mysteries in the Big East.

Are they as good as they looked in December and as tough as they have played at home? Or as bad as they’ve looked lately, and as poor as they’ve played away from New Jersey?

“I wish I could point to something, one or two things, add emphasis to it and hopefully correct it,” said Seton Hall coach Tommy Amaker before the Pirates hosted Syracuse last night.

“We had a stretch where we were winning games and we overachieved a little bit in all honesty. Then we went on the [holiday] break and you’d think that would be a good thing, but sometimes when you’re playing well you don’t want to stop. We lost momentum, whatever it was that was flowing.”

What they might have lost is their confidence.

It’s easy to see why the Pirates have that swashbuckling look about them at home. They’re 10-0 at home games this season, between cavernous Continental Airlines Arena and cozy on-campus Walsh Gym, but they’re just 1-6 on the road with another away game at Boston College on Tuesday. It’s a mystery as to why they play so much better at home considering they average just 6,694, which looks like a small gathering at arena that holds 20,029.

“Its puzzling,” Amaker admits. “You don’t anticipate being undefeated at home and you don’t anticipate being 1-and-something on the road. That’s something we hope to change.”

What has changed for the worse was their play after Dec. 30. The Pirates had also won seven straight games before their loss 65-49 loss Jan. 2 at Providence sent them reeling. The Hall had lost five of six games entering last night’s tilt against the Orangemen. Both teams entered the game tied for seventh in the Big East at 5-5, but that’s about all they have in common because these two teams are in very different situations.

Syracuse was 14-6, ranked 15th in The Post’s Top 25 and a near-lock for the NCAA Tourney. The Pirates had lost five of six, including all three games on their recent road trip to Notre Dame, UConn and Miami. And they may have lost more than games; they may have lost their confidence as well.

“We’re a young team, a fragile team,” Amaker said. “In a couple of games you can lose some confidence as a team. It’s so mental at a certain point.”

It’s also physical. The Pirates, clearly a defensive team, have struggled because their offense has deteriorated. They’d shot less than 40 percent in their last five games.

But Amaker said it isn’t the shooting mechanics that are off or the half-court offense that’s breaking down; he says the Hall’s inconsistent offense was fueled by what was at one point the league’s best defense. Now, with the defense struggling, the offense is struggling, too.

“Our defense has slipped. When we were stopping people we were able to run a little more, get easy baskets, go up for second shots,” Amaker said. “It’s difficult now. It puts too much pressure on your offense.”

Shooting guard Gary Saunders is still leading the team in scoring at 14.8 ppg on .510 shooting, but he scored just two points in the second half of The Hall’s losses at UConn and Miami. And Rimas Kaukenas – 1-for-8 vs. the Hurricanes – was hard-hit by the flu last week and point guard Shaheen Holloway slowed by back spasms. All of that has added up to the Pirates worst slump of the season.

“It’s tough when you invest so much and you don’t get a return for your investment,” Amaker said. “It’s difficult to keep going but I think our guys realize we learned a lot in those three games. There’s a lot of basketball left to play. And I think the month of February will be the ultimate deciding factor [in our season].”