In contrast with the early stumbles in most of the country, New York State, almost from the start, has provided a textbook lesson in how to make the Affordable Care Act work. But it has done so by making some tough decisions.

New York has signed up more than 900,000 people for commercial or government plans, lured 16 insurance companies onto its exchange, provided subsidies for most customers and reduced premiums across the board.

“I have to say that on the whole this is a very savvy bunch of people they have operating the exchange,” Mark P. Scherzer, a lawyer and consumer advocate, said. “It really is a story of something that government could actually do right.”

The state’s success was no accident. It began with a receptive customer base and the benefit of experience, since New York already had some of the country’s most generous insurance coverage for the poor and sick. Resistance to the health exchange among Republicans in the state may, oddly enough, have helped make it more successful.