So important. A contract year. A chance at an NBA title. His opportunity to make some serious money. To solidify his role. To demonstrate his improvement. To earn more playing time. To become revered in Boston legacy. The latest sixth man for the team, the franchise, that made sixth men fashionable.

Frank Ramsey. John Havlicek. Kevin McHale. Bill Walton. Glen Davis. Which name doesn’t belong? You know which one. Including him isn’t fair. Not to the other four players. Not after the season Glen Davis has produced. Even if it all started off so famously.

***

Technically, I suppose, the season didn’t start quite so famously. Not if you consider training camp the season’s beginning. On day one of training camp, Davis spoke out about his role. He was confused about what Doc Rivers wanted him to do. One day, he might play center. The next, power forward. He was expected to post up one quarter, then pick-and-pop the next, and he was expected to switch styles seamlessly. Versatility is a gift, but it is also a curse. If Glen Davis could only bang down low, he would do that solely. If he could only play the perimeter, he would do that solely. But when you can do both, you are asked to do more. You are asked to be more. And Glen Davis wasn’t sure what his role was.

It didn’t take him long to learn it. Ten games into the season, this supposedly confused man fit in like mayonnaise on tuna fish. Patience, Doc Rivers had always preached to Davis. Patience, Davis demonstrated. He allowed the offense to create his shots. He shot well. The last two sentences were not unrelated. He took charges like Shane Battier on steroids. Showed constant energy. Battled on both ends. Davis continued like this for a month or two, churning along, embracing his versatility, earning Doc Rivers’ confidence, earning a growing amount of “Glen Davis for Sixth Man of the Year” support, earning the love and trust of the Boston fan base, earning crunch time minutes at center.

That time seems so long ago.

***

Sometimes, they say, love makes no sense. We sometimes fall in love with people we shouldn’t, with people who are unstable, who will cheat on us, who will drink too heavily, who don’t have enough compassion. Why do we fall in love with these people? Why did Glen Davis fall in love with his jump shot?

At some point this season, Davis became enamored with shots from 16-23 feet. No signs indicate that Davis should love shooting jump shots. Sure, he can make them from time to time, but just because Shaq makes a free throw once in a while doesn’t mean you want him shooting them when the opponent gets a technical foul.

From 16-23 feet, the average NBA player shoots 39.5%. Davis has exceeded that league average only once in his career (2008-’09). He shoots only 35% this season from that range. Yet he shoots more from that spot than all but 23 players in the NBA. Only one player, Jordan Crawford, takes more 16-23 feet jumpers than Davis while making a smaller percentage. Maybe Davis should concentrate his shooting efforts somewhere else. He has increased his effectiveness in the paint, but hasn’t done much to improve his efficiency because he’s shooting too often from 16-23 feet.

Davis shoots 4.6 times per game from that spot, which looks especially confusing when considering he shoots more midrange jumpers than either Paul Pierce (2.8 per game) or Ray Allen (3.3 per game), and just a shade fewer than Kevin Garnett (5.0 per game). Garnett, for comparison’s sake, shoots 47% from that range. His worst shooting season from that range as a Celtic was significantly better than Davis’s best.

Some of Davis’ shots are defensible. He runs a lot of pick-and-pop within the Celtics’ offense, and many of the shots are open. But then there are times when Davis has nine seconds left on the shot clock, and Delonte West comes running to call for the basketball, and Davis waves West off, and the defender is still right in Davis’s mug, and Davis launches a 17-footer anyway, and it inevitably bricks off the rim. As a fan, watching Davis’s shot selection gets tiresome. As a coach, I can’t imagine it’s much better. His rebounding’s not great, either, and his commitment to offensive rebounds has all but disappeared. And the thing is, as Davis continues to struggle, we know the Celtics need to rely on him come playoff time. We know he’ll play a pivotal role.

We can only hope he plays it well.

***

At some point, Davis’ season took a turn for the worse. I would be remiss not to mention his tendinitis, which he says has affected him since the playoffs last year and has caused him to miss games this season. But there are other factors. His shot selection. His confidence, which appears to dwindle with every miss. His willingness (or unwillingness) to let the game come to him, to let the offense dictate his shots, to settle down, to contribute more by doing less.

I continue to believe Davis’ success or failure hinges mostly on his willingness to fit in. When he swings the ball, when he passes down an open shot for a better shot later in the shot clock, when he makes the extra pass, when he cuts swiftly to the hoop to position himself for an easy lay-in, Glen Davis can score effectively and efficiently. But when he starts to get out of himself, forcing shots early in the shot clock and forgetting that he fit in this season because he trusted his offense and his teammates, Davis can disappoint, he can frustrate, he can underwhelm.

Still, he’s a big part of what Boston does. The Celtics play well when Davis plays alongside four starters, and he still figures to play crunch time minutes in the playoffs. He can, and probably will, win Boston games this postseason. But the Celtics need a more consistent effort. Coming into this season, Davis wanted an expanded role. He got it. Now, it’s up to him what he does with it come playoff time.

There’s still time. A bigger contract. An NBA title. A spot in Boston lore. We may never mention Davis among Boston’s other elite sixth men, among the McHales and Havliceks and Waltons, but that’s nothing to cry about. There’s still so much he can accomplish, so much he can attain. There’s still so much the Celtics need from Glen Davis.