Even deeper anxieties, some of the couples said, have come not from revealing their private lives to strangers but to real-life family, colleagues and, in one subject’s case, current and past students.

During filming for Season 3, Josh Elson, a high school music teacher, became so worried about the exposure that he and his wife, Molly, told the producers they wanted to quit. They had just had a particularly explosive session, and it suddenly sunk in that their issues could be put out there for the world to see.

Producers met them at a coffee shop in their neighborhood and talked them out of quitting, Molly said, by emphasizing how their story could help viewers navigate their own marriages — and reminding them that they had signed a contract.

“They made us feel like they weren’t going to exploit our story,” Josh said, adding that their decision to continue the sessions was a crossroads, after which the treatment started to come into focus.

Five years in, the showrunners say that what started as a far-fetched experiment has become a well-oiled machine, complete with a sort of instruction manual to teach crew members about the show’s philosophy and how to approach its subjects. “There’s a really intense culture of respect and, really, reverence for what they’re bringing in,” Kriegman said.

Would the producers be open to going on the show themselves? Two out of three said they would.

“I don’t think I’m brave enough,” Kriegman, the holdout, replied.