It’s always painful to watch a great player leave a team, but it can be worse when they stay.

The one bitter part of last year for White Sox fans was watching the team win its first world championship in more than 80 years while the greatest player in team history, Frank Thomas, was limited to just a little more than a month of action by injuries, a time in which he hit just .219. He finally won his ring, but for him to do so without even taking the field in the playoffs made the whole thing feel a bit hollow.

Even that was better than what took place after the season; Thomas complained about being disrespected, the general manager called him an idiot, and he ended up in the gold and green colors of the Oakland Athletics. It would have been better had the team and the player severed their relationship long before; but in trying to do the right thing and show mutual loyalty, they ruined the very thing they were trying to preserve.

Mets fans will never have to feel that way about Mike Piazza. Just as Thomas is the greatest player in White Sox history, Piazza is, easily, the greatest position player in Mets history. The Mets, though, made the difficult but correct decision last year and chopped the limb off cleanly rather than painfully sawing it off, by bringing Piazza back in some reduced role or staying with him as the regular catcher despite the hard way he’d aged. Even with Piazza having a fine season, it was the right call.

In just the cold baseball sense, it was clearly the right call at the time and was worth it even with Piazza staying healthy and productive this year. His .297 AVG/.354 OBA/.525 SLG line is comparable to Paul LoDuca’s .322/.366/.427 line, enough to offset the sense one has that LoDuca’s bat control, opposite-field stroke, and relative quickness fit the Mets’ lineup a bit better than Piazza’s lumbering right-handed power. But the difference behind the plate is at least as significant as the difference at it.

Piazza never was criticized for his effort, but seeing him behind the Shea dish last night reminded you of all the things he couldn’t do over the last few years, like run up the line or spear balls to his right or throw out any baserunners at all. LoDuca is simply a better player at this point in their careers.

More important than that, though, is the intangible effect a player like Piazza has on the feel of a team. He was never the vocal leader of the Mets, but he was always their symbol. First as a highlypriced acquisition who stunned everyone in New York by playing a gritty game worthy of a 62nd-round draft pick, and later as the lethargic, immobile, and only intermittently available anchor of a team whose time had passed.

Much like Thomas, as a reminder of the days when the White Sox were nothing but a wall of right-handed power hitters, seemed last year like an old ghost haunting a young team designed in a different image, it’s somehow impossible to imagine Piazza fitting into the complete reinvention of the Mets that’s taken place this year. There cannot be two players with less in common than Piazza and Jose Reyes, and it was the right decision to allow the one to leave so that the other could become the new symbol of the team.

With the team winning, the urgent necessity of Piazza’s departure — the need for him to leave for the team to move forward on the field and in the hearts and minds of the fans — becomes softened, and all anyone remembers are the good times, of which there were many. The roaring ovation he received last night was every bit due to the man who, more than any other player, drove the Mets’ resurgence in the late ’90s, who finally wrenched them out of the Davey Johnson era and into the present. Bret Saberhagen couldn’t do it, Vince Coleman couldn’t do it, Jason Isringhausen couldn’t do it, and neither could Rey Ordonez; it took a truly great player, one with magnificent flair, to give a team that had long since forfeited its dignity a sense of pride. That, rightly, is what everyone was applauding.

But close as he came, with one of those awesomely balanced and powerful right-handed cuts, to crushing one of the massive opposite-field home runs that every single fan in the park wanted to see in his first at-bat, it ended as a near-double landing in foul territory. That’s pretty much the story of why he’s gone and why he should be gone. The Mets had many years in which they tried to do the right thing, and it never ended well. This season is playing out the way it is because they finally realized that the right thing to do is to win. If they’d realized that a few years sooner, Piazza might have that ring after all.

tmarchman@nysun.com