A new fly-on-the-wall documentary begins next week. Is it inevitable that the people it follows will look like morons, asks Shane Hegarty.

You have a great idea. You start a business. You go in with a couple of other people, put your money and your reputation on the line. You have a big launch and get lots of publicity. Then you sit back and wait for the money to roll in.

It goes horribly wrong. Nobody buys your product. You lose your money and your reputation. You argue with your partners and have to let the staff go. You pack up the business and go away to try to forget about it - best to put it behind you. Then, a year later, a fly-on-the-wall documentary broadcasts the sorry chapter to the nation.

"I don't think I've seen a fly-on-the-wall documentary in which the participants don't look like complete morons," says John Ryan. It's a brave statement, given that on Tuesday he stars in a documentary following Stars On Sunday, his ill-fated newspaper venture. Any Given Sunday charts the venture's failure with a prurience and rawness the public has come to expect of fly-on-the-wall documentaries.

The idea had been to allow the film to be made so that when it was broadcast it would boost circulation. Of course, the idea had also been that the newspaper would have lasted longer than the nine issues. "I assumed it would be a less than flattering portrayal," he says. "Not that it was wittingly a stitch-up on their part, but I do think that TV people need to set up villains and good guys. I think it's also the very nature of them that if you follow someone for a day or two you're just going to see a weird side to them or a side that's not so appealing."

Television is awash with these programmes. The original reality television, the fly-on-the-wall genre has never been more prolific, thanks to the development of digital cameras and a never-ending supply of subjects, of people willing to put their dignity and reputation on the line. Tony Smith was another who did it, allowing the cameras to record him as he left his job and his life in Drogheda and followed his dream of building a tourist hostel on Inishbofin. The subsequent documentary, Island Life, was broadcast last year.

"I was anxious," says Smith. "I didn't know what it would entail. It was only 27 minutes long, there would be only a tiny percentage of our character on display and we could end up looking like the biggest eejits around. I was putting me, my family, my wife and kids up, and I felt exposed. But I looked at it as an opportunity, and it did work out as a good balance. They saw the real McCoy and it did the world of good for us."

Smith only agreed to do it, he says, because he initially thought it was a prank being played by friends. Approached by the producer of the documentary while having a drink in Donegal, he only fully accepted the idea when the camera crew arrived on the island. Yet, he says, he soon began to ignore the camera's presence. The final film included an interview with his now wife, Geraldine, that she didn't remember doing. When up against it to get the hostel built, he says, he just didn't notice the cameras. "There were the odd times when I'd lift my head and the camera would almost hit me on the head, and sometimes you'd let a bit of a roar out of you."

Despite wondering if the moment would arise, Smith says he didn't ask for the camera to be turned off. He had also been given a camcorder to film his progress when the crew wasn't around, however, and it gave him a measure of control.

"I was definitely tempted not to put stuff on camera. For those home parts, I would finish after a day's work and I would be aching. I lost two and a half stone during that period, and then I would have to go home, wrecked, and sit down and be expected to spill my guts to a camera. I found it occasionally intrusive. So that didn't happen as often as they might have hoped."

Ryan says that he, too, was amazed the camera had been present at certain times, that he had very quickly stopped noticing the crew. Yet there are a couple of moments in Any Given Sunday when the camera is not allowed in. The meeting that winds up the company is off limits, and the camera crew were asked to leave as the management informed staff of the closure.

According to Stuart Switzer, of producers Coco Television, it took a little time for the Stars On Sunday team to forget the camera was there. "It took them about two or three days to settle. They kept talking down the lens, and we did say it to them that they were not to be playing to us. But they do forget about the camera. When you're dealing with the reality of people's lives, decisions that affect their future career and that are more important than the camera in the background capturing their reactions, then ego fades away, commercial realities dawn and they worry less about how people will see them in a few months."

The genre, he says, is based on trust between subject and documentary-maker. Both need to be honest, and the subject needs to trust that the truth will not be distorted in the editing suite. "We had a handshake on it," says Switzer, "saying we'll be fair to you if you're fair to us. We're not interested in a story that didn't happen."

He admits, though, that a good narrative was important. "We hoped it wouldn't be a sick puppy, crawling along, doing just enough to cover costs. We wanted glory or liquidation, a good end in a dispassionate way. I mean, if it had done well and someone had come in and bought the company, then that would have been a great ending."

Adrian McCarthy has made some of Ireland's best contemporary documentaries - Dead Silence, about the effects of BSE on a farm, and Living The Revolution, following the Sinn Féin TD Martin Ferris through his election campaign - and agrees that there can be mixed emotions from those behind the camera.

"For me it's important if there is a bit of drama in there, because people are dealing with conflicts within their life, and it's fascinating to see how they deal with these obstacles and issues. And some film-makers probably do want things to fall apart - and in a way the viewer does, too. A lot, though, depends on whether it was a good idea when you go in. If you're looking for misery you will certainly find it."

His latest film, on road deaths, brought him face to face with horrific situations: raw fly-on-the-wall, when it can be at its most intrusive and yet most instructive. "It's important for people to feel uncomfortable," says McCarthy. "What gets [the viewers\] is when they want the camera to pull away now but you want them to think, you don't want things to be overly simplistic. And even when it's very hard to keep filming it's important to do so."

John Ryan has seen Any Given Sunday, and his nerves and pride seem to have survived the experience. "I was so pathetically grateful that it wasn't a stitch-up, that I wasn't edited in such a way, because I know how you can edit things. In the end, though, I was a lot less embarrassed than I thought I would be."

When Island Life was broadcast, Tony Smith and his family drew the curtains and watched through their fingers. "It was quite emotional, but I was very satisfied. It did us proud. Afterwards, we had a big party with friends. I couldn't have bought the PR."

Any Given Sunday begins on RTÉ1 at 10.10pm on Tuesday, concluding on May 6th