Which leads us to the next question: If the planned new repairs would be as safe and durable without requiring closing the line, why didn’t anyone think of them before? Shouldn't someone downstream of the governor have thought to bring in outside experts for a fresh look, given the disruptive stakes?

Some people are skeptical about this new plan, in fact, precisely because it was driven by Governor Cuomo. That’s good. Without skepticism, society collapses. But this entire episode illustrates a failure to be skeptical. And it shows us the risks of ignoring what it means to fail, at scale, in a booming city that grows every month. It didn’t have to be the governor asking for a better way. But no one else did.

Until then, the new array of repairs had not been considered by the in-house engineers at the Metropolitan Transportation Authority, the WSP consultants or others involved in the project. Andy Byford, the president of New York City Transit, said he was conducting an independent review of the plan and would not sign on unless he was convinced of its safety and durability. That said, he is enthusiastic about its prospects. “I own the risk,” Mr. Byford said. “I am the president, the accountable person. This is my job.”

Anyone on the M.T.A. board could have demanded alternatives. Mr. Cuomo appoints six of the 14 voting members, and by force of personality, he has driven a number of projects, including this one — at the last minute — and pushing construction of the Second Avenue line.

You can find representatives of eight other public officials on the authority’s board, including the mayor of New York. Even more power is held by a virtually unknown committee of four, any one of whom can veto the entire capital budget. On this committee are the speaker of the State Assembly, the State Senate majority leader, the mayor and the governor.