The plan was always about size, not just to overthrow the Lakers but also to pound the Heat at their weakest position, to limit Dwight Howard as much as possible, and to physically dominate lesser frontcourts. Rajon Rondo is great, of course, and Paul Pierce and Ray Allen, obviously, can still play. But the 2010-’11 Celtics were constructed to overwhelm teams with length, tenacity and toughness.

The Celtics added brawn and bulk this past offseason, signing the O’Neal brothers — we suspected, at least — because they knew, without a deep stable of big men, one injury to Kendrick Perkins could mean the difference between winning and losing a championship. Instead of sticking to that plan, the Celtics move forward with a center rotation consisting of A) a 6’9, round mound of no rebound who takes charges quite well but, again, is 6’9, B) two way-past-their-prime O’Neals, who aren’t healthy now and may never be, and C) a chair-throwing Nenad who can’t rebound and whose bald spot makes him look far older than his 27 years. So I ask you: what happened to the plan, to the blueprint that was supposed to bring Boston a championship?

Before I move forward, let me admit that I loved Kendrick Perkins as a player, as a person, and as a reporter on the few occasions I got to interview Perkins. But I’m not allowing that to cloud my judgment of this trade. The thoughts in this column are unbiased, and the thing I care most about moving forward — though I will miss Perk, as a fan — is how this trade affects the Boston Celtics’ chances to win a championship.

There is a chance this trade works out perfectly. If the O’Neals both (miraculously) return to good health, the Celtics will remain deep, strong, big, and tough. They will still have a frontcourt rotation that rivals ( and, mostly, puts to shame) any other team’s. Even if only one of the O’Neals returns, a Glen Davis-Jermaine/Shaq-Nenad Krstic center rotation can hold its own. And the C’s will have added Jeff Green to the bench, a bench that clearly needed some help and has been inconsistent (to say it nicely) this entire season.

There’s a line of reasoning, and it holds some clout, which says the Celtics were fine without Perkins over the first half of the season. That’s true. Their defense survived (thrived, even), and Shaq fit right in with the C’s starters. When Perkins returned, the Celtics were already 33-10 and ahead of the entire Eastern Conference. The Celtics can win without Perkins, there’s no question. But during most of that time, the O’Neals were (relatively) healthy.

Doesn’t this new plan rely far too heavily on two O’Neals, who have COMBINED to play in only 53 games this season? Two O’Neals whose bodies have proven incredibly unreliable? Two O’Neals who can’t stay on the court and can’t reasonably be expected to provide nightly support? Two O’Neals whose careers — not just seasons — have been marred by injury after injury?

What happens if both O’Neals miss a playoff game? Are you happy about the thought of Glen Davis, Troy Murphy and Nenad Krstic trotting out alongside KG to battle Pau Gasol and Andrew Bynum? Or Dwight Howard? Or even trying to overwhelm the Heat’s thin frontcourt (which wouldn’t look nearly as thin against the Davis-Murphy-Krstic trio)? Do those thoughts intrigue you? I doubt it. The Celtics were built on size and toughness. Unless the O’Neals get healthy for the stretch run, the Celtics lost a large part of their identity by shipping Kendrick Perkins away. Kevin Garnett remains a Boston Celtics, and he’s their heart. But Boston’s imposing frontcourt will no longer impose, unless the O’Neals are healthy. An “unless” that — if you’ve been paying attention to the C’s injury list — doesn’t inspire hope.

That the Celtics’ championship hopes may now rest on the O’Neal brothers’ health isn’t even what bothers me most. No, I’m most bothered that the Celtics didn’t have to take such a big risk. If they sat steady at the trade deadline, without making a single move, the Celtics would have remained the favorites to win the NBA championship. They had a tried and true method of winning. If Garnett had stayed healthy in ’09, and Perk in ’10, the Celtics possibly could have been three-time defending champions right now. And they did all that winning with Perk as their center, with an unapologetic mean streak as their calling card.

When you thought of the Celtics’ championship hopes yesterday at 2:00 p.m., you knew what the Celtics were. A rugged crew. A team that rose to every challenge, even in defeat. A team that was almost always physically and mentally tougher than its opponent, and never, ever backed down. They were Kevin Garnett screaming his head off, and they were Kendrick Perkins standing by his side to provide the muscle and intimidation (not to mention the wondrous post defense). They were a well-oiled machine consisting of players who knew each other in and out, and had never lost a playoff series when healthy.

Now? The Celtics may be looking forward to 40 minutes of center Glen Davis (who, I remind you, is 6’9) in every playoff game, which may not prove destructive but certainly isn’t ideal. The Celtics may use Nenad Krstic, and his underwhelming 12.2 rebound rate, as Davis’ lone backup. If the O’Neals aren’t healthy — and is there any reasonable reason to believe they will be? — the Celtics won’t be big, bad and strong, like they had planned to be ever since losing Game 7 and seeing the Lakers celebrate an NBA title. They won’t push around opponents to the same extent, and they certainly won’t scowl as much. Whether the Celtics scowl doesn’t seem important, but Glen Davis and Nenad Krstic don’t intimidate people. Kendrick Perkins does. Shaq and Jermaine, if healthy (such a brutal if), might.

Yesterday at 2:00 p.m., the Boston Celtics were the favorites to win the 2011 NBA championship. When the season’s all said and done, they still might win a title. I’m not ruling that out, not by any means. Jeff Green, for all the intelligent people (rightfully) saying he’s overrated, is still a versatile, athletic player who will improve Boston’s bench and give Doc Rivers more options. Nenad Krstic, for all my complaints about his soft nature, possesses a few worthy skills and isn’t a terrible option off the bench. The O’Neals might return to full health, and Perkins might prove to be just what Danny Ainge banked that he would be: expendable.

But why risk it? Why wake up on February 24, the day of the trade deadline, and decide, “Ya know what? Let’s change everything today — our philosophy, our starting lineup, our chemisty. Let’s just change it all. Even though we’re NBA favorites if we just stand pat, and even better than that if we keep our core intact while trading for a Shane Battier type (or even an Anthony Parker type), let’s ship Kendrick Perkins away. Let’s roll the dice.”? Why?

On the periphery, you can argue the trade makes sense. Perkins, for everything he brought the Celtics, had flaws, and — if the O’Neals are still alive by the time the postseason rolls around — Perk’s presence would have made for a very full frontcourt. They had a gaping hole at backup small forward, and Green fills that. The Celtics may also consider Green a better piece for the future than Perk, though that reasoning could be argued and this shouldn’t be about the future. But there’s a reason the Celtics imported so much size: They learned first hand how a single injury can impact an NBA championship. They learned first hand how much they needed Kendrick Perkins. So they implemented a plan focused primarily on adding size, and more size.

Yesterday, the Celtics ditched that plan and decided to go a different route. It wasn’t because they didn’t think they could sign Kendrick Perkins; he told me he couldn’t see himself anyplace but Boston, and a report said he would have accepted a $30 million contract from Boston (which, for a player of Perk’s caliber and size, amounts to chump change). Even if the Celtics did fear losing Perk for nothing, trying to win a title with him now STILL made sense. It wasn’t because they worried about his health, because they offered him a contract extension a few weeks ago. It wasn’t because the current plan had proven itself the wrong plan, because the Celtics, with Perk, were the NBA’s favorites. It was because Danny Ainge felt adding Jeff Green and Nenad Krstic, while subtracting Kendrick Perkins and Nate Robinson, would improve the Boston Celtics.

You know what they say: If it ain’t broke, trade your 6’11, tough-as-nails player away, while risking your teams’ very identity in the process, and potentially hinging your team’s title aspirations on the health of two immensely fragile old men. The Celtics didn’t have to take this risk. That’s what I don’t understand, no matter how hard I try.