But the story of the Poor Clares’ monastery — or as it’s known on the books of the Boston Planning Department, 920 Centre Street — is, at least for now, a case study on how housing doesn’t get built in this city.

It’s a story about how one midsized project with everything going for it — a world-class architect, a brilliant landscape designer, and a developer willing to make one compromise after another to the size and layout of the plan — still can’t move the needle in the face of one powerful opponent.

Well, make that one powerful opponent who has the ear of City Hall.

Faced with dwindling numbers in their order (they were down to 10 in 2022) and a Vatican mandate to consolidate, the sisters decided to sell their 2.8-acre parcel and the aging monastery building to developer John Holland. The building, which they had occupied since 1934, was expensive to heat and in need of extensive repairs.

They relocated to Westwood in 2023, hoping to expand those quarters to accommodate another 10 nuns from around the country as soon as the sale of the Jamaica Plain property became final, contingent on the approval of its redevelopment.

They’re still waiting.

The former monastery is neighbor to the Arnold Arboretum, land owned by the city but under a renewable 1,000-year lease to Harvard University. And no question, the 281-acre parcel is a tree-filled treasure for researchers and picnickers alike. Just try getting near the place on Lilac Sunday.

But the Arboretum, or rather its director, William Friedman, a Harvard evolutionary biology professor, has emerged as a powerful foe.

“The development has been part of the city’s planning process for nearly five years and has undergone several revisions,” Sr. Mary Veronica McGuff, the order’s abbess, wrote in a letter to Mayor Michelle Wu in January and shared with the editorial board. “We are very disappointed to learn that the main obstacle is … the Arnold Arboretum.”

She revealed that the order had earlier offered to sell the property to the Arboretum, but was rebuffed.

“It’s upsetting that our progress is now being hindered by an institution that declined the opportunity to take stewardship of the land and is now making unreasonable demands for its redevelopment,” she said in the letter.

In fact, its market rate condo component, once slated to be five stories high, has been reduced to four stories. Those 38 senior rental units planned for the monastery building will include 25 affordable units.

Project architect David Hacin, winner of the Boston Preservation Alliance’s 2022 President’s Award for Excellence, is equally bewildered.

“I don’t understand how a project that is so good on so many levels is being held up for years, literally, over asks that seem, to me, completely unreasonable,” Hacin told Globe business reporter Catherine Carlock. “If we can’t build five-story buildings, how are we going to solve the housing crisis?”

How indeed.

The developers have done shadow studies, a sunlight analysis, and tree root studies to convince Arboretum officials that the planned housing would do no damage to the magnolia tree roots on the perimeter of Harvard’s grounds, which seem to be their main bone of contention.

The project’s landscape architect Mikyoung Kim has surely not acquired her international reputation for “ecological restoration” by murdering magnolia trees.

Friedman has met with Boston’s planning chief, Kairos Shen, but as of Thursday the sisters have not yet been granted a similar opportunity. Nor have they heard from either Wu or Shen (who was copied in on the Jan. 12 letter) since they made their appeal for help “in finding a solution that allows this project to move forward and for our community to finally settle into our new home.”

In a statement to the Globe editorial board, Wu said, “Large properties like 920 Centre Street are significant housing sites for Boston, and we are working actively with all parties to advance a plan that would deliver homes our city needs.”

For the past year, experts have been warning that the slumping number of building permits in Greater Boston — down 44 percent last year from four years ago — do not bode well for an increase in the future housing supply. That dearth in supply is driving up prices and rents.

And while the Wu administration is quick to blame President Trump’s tariffs and rising costs for the construction slump, it fails to look in the mirror. Enabling the kind of Not In My Back Yard obstructionism that is keeping a good project on the drawing boards for years will never get Boston the kind of housing it needs to keep pace with demand and allow this city to thrive.

Editorials represent the views of the Boston Globe Editorial Board. Follow us @GlobeOpinion.